webmvc.adoc

Spring Web MVC

Spring Web MVC is the original web framework built on the Servlet API and has been included in the Spring Framework from the very beginning. The formal name, “Spring Web MVC,” comes from the name of its source module ({spring-framework-main-code}/spring-webmvc[spring-webmvc]), but it is more commonly known as “Spring MVC”.

Parallel to Spring Web MVC, Spring Framework 5.0 introduced a reactive-stack web framework whose name, “Spring WebFlux,” is also based on its source module ({spring-framework-main-code}/spring-webflux[spring-webflux]). This section covers Spring Web MVC. The next section covers Spring WebFlux.

For baseline information and compatibility with Servlet container and Java EE version ranges, see the Spring Framework Wiki.

DispatcherServlet

WebFlux

Spring MVC, as many other web frameworks, is designed around the front controller pattern where a central Servlet, the DispatcherServlet, provides a shared algorithm for request processing, while actual work is performed by configurable delegate components. This model is flexible and supports diverse workflows.

The DispatcherServlet, as any Servlet, needs to be declared and mapped according to the Servlet specification by using Java configuration or in web.xml. In turn, the DispatcherServlet uses Spring configuration to discover the delegate components it needs for request mapping, view resolution, exception handling, and more.

The following example of the Java configuration registers and initializes the DispatcherServlet, which is auto-detected by the Servlet container (see Servlet Config):

Java

public class MyWebApplicationInitializer implements WebApplicationInitializer {

	@Override
	public void onStartup(ServletContext servletContext) {

		// Load Spring web application configuration
		AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
		context.register(AppConfig.class);

		// Create and register the DispatcherServlet
		DispatcherServlet servlet = new DispatcherServlet(context);
		ServletRegistration.Dynamic registration = servletContext.addServlet("app", servlet);
		registration.setLoadOnStartup(1);
		registration.addMapping("/app/*");
	}
}

Kotlin

class MyWebApplicationInitializer : WebApplicationInitializer {

	override fun onStartup(servletContext: ServletContext) {

		// Load Spring web application configuration
		val context = AnnotationConfigWebApplicationContext()
		context.register(AppConfig::class.java)

		// Create and register the DispatcherServlet
		val servlet = DispatcherServlet(context)
		val registration = servletContext.addServlet("app", servlet)
		registration.setLoadOnStartup(1)
		registration.addMapping("/app/*")
	}
}

Note	In addition to using the ServletContext API directly, you can also extend AbstractAnnotationConfigDispatcherServletInitializer and override specific methods (see the example under Context Hierarchy).

Note	For programmatic use cases, a GenericWebApplicationContext can be used as an alternative to AnnotationConfigWebApplicationContext. See the {api-spring-framework}/web/context/support/GenericWebApplicationContext.html[GenericWebApplicationContext] javadoc for details.

The following example of web.xml configuration registers and initializes the DispatcherServlet:

<web-app>

	<listener>
		<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
	</listener>

	<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>/WEB-INF/app-context.xml</param-value>
	</context-param>

	<servlet>
		<servlet-name>app</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<init-param>
			<param-name>contextConfigLocation</param-name>
			<param-value></param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
	</servlet>

	<servlet-mapping>
		<servlet-name>app</servlet-name>
		<url-pattern>/app/*</url-pattern>
	</servlet-mapping>

</web-app>

Note

Spring Boot follows a different initialization sequence. Rather than hooking into the lifecycle of the Servlet container, Spring Boot uses Spring configuration to bootstrap itself and the embedded Servlet container. Filter and Servlet declarations are detected in Spring configuration and registered with the Servlet container. For more details, see the Spring Boot documentation.

Context Hierarchy

DispatcherServlet expects a WebApplicationContext (an extension of a plain ApplicationContext) for its own configuration. WebApplicationContext has a link to the ServletContext and the Servlet with which it is associated. It is also bound to the ServletContext such that applications can use static methods on RequestContextUtils to look up the WebApplicationContext if they need access to it.

For many applications, having a single WebApplicationContext is simple and suffices. It is also possible to have a context hierarchy where one root WebApplicationContext is shared across multiple DispatcherServlet (or other Servlet) instances, each with its own child WebApplicationContext configuration. See Additional Capabilities of the ApplicationContext for more on the context hierarchy feature.

The root WebApplicationContext typically contains infrastructure beans, such as data repositories and business services that need to be shared across multiple Servlet instances. Those beans are effectively inherited and can be overridden (that is, re-declared) in the Servlet-specific child WebApplicationContext, which typically contains beans local to the given Servlet. The following image shows this relationship:

The following example configures a WebApplicationContext hierarchy:

Java

public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {

	@Override
	protected Class<?>[] getRootConfigClasses() {
		return new Class<?>[] { RootConfig.class };
	}

	@Override
	protected Class<?>[] getServletConfigClasses() {
		return new Class<?>[] { App1Config.class };
	}

	@Override
	protected String[] getServletMappings() {
		return new String[] { "/app1/*" };
	}
}

Kotlin

class MyWebAppInitializer : AbstractAnnotationConfigDispatcherServletInitializer() {

	override fun getRootConfigClasses(): Array<Class<*>> {
		return arrayOf(RootConfig::class.java)
	}

	override fun getServletConfigClasses(): Array<Class<*>> {
		return arrayOf(App1Config::class.java)
	}

	override fun getServletMappings(): Array<String> {
		return arrayOf("/app1/*")
	}
}

Tip	If an application context hierarchy is not required, applications can return all configuration through getRootConfigClasses() and null from getServletConfigClasses().

The following example shows the web.xml equivalent:

<web-app>

	<listener>
		<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
	</listener>

	<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>/WEB-INF/root-context.xml</param-value>
	</context-param>

	<servlet>
		<servlet-name>app1</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<init-param>
			<param-name>contextConfigLocation</param-name>
			<param-value>/WEB-INF/app1-context.xml</param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
	</servlet>

	<servlet-mapping>
		<servlet-name>app1</servlet-name>
		<url-pattern>/app1/*</url-pattern>
	</servlet-mapping>

</web-app>

Tip	If an application context hierarchy is not required, applications may configure a “root” context only and leave the contextConfigLocation Servlet parameter empty.

Special Bean Types

WebFlux

The DispatcherServlet delegates to special beans to process requests and render the appropriate responses. By “special beans” we mean Spring-managed Object instances that implement framework contracts. Those usually come with built-in contracts, but you can customize their properties and extend or replace them.

The following table lists the special beans detected by the DispatcherServlet:

Bean type	Explanation
HandlerMapping	Map a request to a handler along with a list of interceptors for pre- and post-processing. The mapping is based on some criteria, the details of which vary by HandlerMapping implementation. The two main HandlerMapping implementations are RequestMappingHandlerMapping (which supports @RequestMapping annotated methods) and SimpleUrlHandlerMapping (which maintains explicit registrations of URI path patterns to handlers).
HandlerAdapter	Help the DispatcherServlet to invoke a handler mapped to a request, regardless of how the handler is actually invoked. For example, invoking an annotated controller requires resolving annotations. The main purpose of a HandlerAdapter is to shield the DispatcherServlet from such details.
HandlerExceptionResolver	Strategy to resolve exceptions, possibly mapping them to handlers, to HTML error views, or other targets. See Exceptions.
ViewResolver	Resolve logical String-based view names returned from a handler to an actual View with which to render to the response. See View Resolution and [mvc-view].
LocaleResolver, LocaleContextResolver	Resolve the Locale a client is using and possibly their time zone, in order to be able to offer internationalized views. See Locale.
ThemeResolver	Resolve themes your web application can use — for example, to offer personalized layouts. See Themes.
MultipartResolver	Abstraction for parsing a multi-part request (for example, browser form file upload) with the help of some multipart parsing library. See Multipart Resolver.
FlashMapManager	Store and retrieve the “input” and the “output” FlashMap that can be used to pass attributes from one request to another, usually across a redirect. See Flash Attributes.

Web MVC Config

WebFlux

Applications can declare the infrastructure beans listed in Special Bean Types that are required to process requests. The DispatcherServlet checks the WebApplicationContext for each special bean. If there are no matching bean types, it falls back on the default types listed in {spring-framework-main-code}/spring-webmvc/src/main/resources/org/springframework/web/servlet/DispatcherServlet.properties[DispatcherServlet.properties].

In most cases, the MVC Config is the best starting point. It declares the required beans in either Java or XML and provides a higher-level configuration callback API to customize it.

Note	Spring Boot relies on the MVC Java configuration to configure Spring MVC and provides many extra convenient options.

Servlet Config

In a Servlet 3.0+ environment, you have the option of configuring the Servlet container programmatically as an alternative or in combination with a web.xml file. The following example registers a DispatcherServlet:

Java

import org.springframework.web.WebApplicationInitializer;

public class MyWebApplicationInitializer implements WebApplicationInitializer {

	@Override
	public void onStartup(ServletContext container) {
		XmlWebApplicationContext appContext = new XmlWebApplicationContext();
		appContext.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml");

		ServletRegistration.Dynamic registration = container.addServlet("dispatcher", new DispatcherServlet(appContext));
		registration.setLoadOnStartup(1);
		registration.addMapping("/");
	}
}

Kotlin

import org.springframework.web.WebApplicationInitializer

class MyWebApplicationInitializer : WebApplicationInitializer {

	override fun onStartup(container: ServletContext) {
		val appContext = XmlWebApplicationContext()
		appContext.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml")

		val registration = container.addServlet("dispatcher", DispatcherServlet(appContext))
		registration.setLoadOnStartup(1)
		registration.addMapping("/")
	}
}

WebApplicationInitializer is an interface provided by Spring MVC that ensures your implementation is detected and automatically used to initialize any Servlet 3 container. An abstract base class implementation of WebApplicationInitializer named AbstractDispatcherServletInitializer makes it even easier to register the DispatcherServlet by overriding methods to specify the servlet mapping and the location of the DispatcherServlet configuration.

This is recommended for applications that use Java-based Spring configuration, as the following example shows:

Java

public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {

	@Override
	protected Class<?>[] getRootConfigClasses() {
		return null;
	}

	@Override
	protected Class<?>[] getServletConfigClasses() {
		return new Class<?>[] { MyWebConfig.class };
	}

	@Override
	protected String[] getServletMappings() {
		return new String[] { "/" };
	}
}

Kotlin

class MyWebAppInitializer : AbstractAnnotationConfigDispatcherServletInitializer() {

	override fun getRootConfigClasses(): Array<Class<*>>? {
		return null
	}

	override fun getServletConfigClasses(): Array<Class<*>>? {
		return arrayOf(MyWebConfig::class.java)
	}

	override fun getServletMappings(): Array<String> {
		return arrayOf("/")
	}
}

If you use XML-based Spring configuration, you should extend directly from AbstractDispatcherServletInitializer, as the following example shows:

Java

public class MyWebAppInitializer extends AbstractDispatcherServletInitializer {

	@Override
	protected WebApplicationContext createRootApplicationContext() {
		return null;
	}

	@Override
	protected WebApplicationContext createServletApplicationContext() {
		XmlWebApplicationContext cxt = new XmlWebApplicationContext();
		cxt.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml");
		return cxt;
	}

	@Override
	protected String[] getServletMappings() {
		return new String[] { "/" };
	}
}

Kotlin

class MyWebAppInitializer : AbstractDispatcherServletInitializer() {

	override fun createRootApplicationContext(): WebApplicationContext? {
		return null
	}

	override fun createServletApplicationContext(): WebApplicationContext {
		return XmlWebApplicationContext().apply {
			setConfigLocation("/WEB-INF/spring/dispatcher-config.xml")
		}
	}

	override fun getServletMappings(): Array<String> {
		return arrayOf("/")
	}
}

AbstractDispatcherServletInitializer also provides a convenient way to add Filter instances and have them be automatically mapped to the DispatcherServlet, as the following example shows:

Java

public class MyWebAppInitializer extends AbstractDispatcherServletInitializer {

	// ...

	@Override
	protected Filter[] getServletFilters() {
		return new Filter[] {
			new HiddenHttpMethodFilter(), new CharacterEncodingFilter() };
	}
}

Kotlin

class MyWebAppInitializer : AbstractDispatcherServletInitializer() {

	// ...

	override fun getServletFilters(): Array<Filter> {
		return arrayOf(HiddenHttpMethodFilter(), CharacterEncodingFilter())
	}
}

Each filter is added with a default name based on its concrete type and automatically mapped to the DispatcherServlet.

The isAsyncSupported protected method of AbstractDispatcherServletInitializer provides a single place to enable async support on the DispatcherServlet and all filters mapped to it. By default, this flag is set to true.

Finally, if you need to further customize the DispatcherServlet itself, you can override the createDispatcherServlet method.

Processing

WebFlux

The DispatcherServlet processes requests as follows:

• The WebApplicationContext is searched for and bound in the request as an attribute that the controller and other elements in the process can use. It is bound by default under the DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE key.

• The locale resolver is bound to the request to let elements in the process resolve the locale to use when processing the request (rendering the view, preparing data, and so on). If you do not need locale resolving, you do not need the locale resolver.

• The theme resolver is bound to the request to let elements such as views determine which theme to use. If you do not use themes, you can ignore it.

• If you specify a multipart file resolver, the request is inspected for multiparts. If multiparts are found, the request is wrapped in a MultipartHttpServletRequest for further processing by other elements in the process. See Multipart Resolver for further information about multipart handling.

• An appropriate handler is searched for. If a handler is found, the execution chain associated with the handler (preprocessors, postprocessors, and controllers) is run to prepare a model for rendering. Alternatively, for annotated controllers, the response can be rendered (within the HandlerAdapter) instead of returning a view.

• If a model is returned, the view is rendered. If no model is returned (maybe due to a preprocessor or postprocessor intercepting the request, perhaps for security reasons), no view is rendered, because the request could already have been fulfilled.

The HandlerExceptionResolver beans declared in the WebApplicationContext are used to resolve exceptions thrown during request processing. Those exception resolvers allow customizing the logic to address exceptions. See Exceptions for more details.

For HTTP caching support, handlers can use the checkNotModified methods of WebRequest, along with further options for annotated controllers as described in HTTP Caching for Controllers.

You can customize individual DispatcherServlet instances by adding Servlet initialization parameters (init-param elements) to the Servlet declaration in the web.xml file. The following table lists the supported parameters:

Table 1. DispatcherServlet initialization parameters

Parameter	Explanation
contextClass	Class that implements ConfigurableWebApplicationContext, to be instantiated and locally configured by this Servlet. By default, XmlWebApplicationContext is used.
contextConfigLocation	String that is passed to the context instance (specified by contextClass) to indicate where contexts can be found. The string consists potentially of multiple strings (using a comma as a delimiter) to support multiple contexts. In the case of multiple context locations with beans that are defined twice, the latest location takes precedence.
namespace	Namespace of the WebApplicationContext. Defaults to [servlet-name]-servlet.
throwExceptionIfNoHandlerFound	Whether to throw a NoHandlerFoundException when no handler was found for a request. The exception can then be caught with a HandlerExceptionResolver (for example, by using an @ExceptionHandler controller method) and handled as any others. By default, this is set to false, in which case the DispatcherServlet sets the response status to 404 (NOT_FOUND) without raising an exception. Note that, if default servlet handling is also configured, unresolved requests are always forwarded to the default servlet and a 404 is never raised.

Path Matching

The Servlet API exposes the full request path as requestURI and further sub-divides it into contextPath, servletPath, and pathInfo whose values vary depending on how a Servlet is mapped. From these inputs, Spring MVC needs to determine the lookup path to use for handler mapping, which is the path within the mapping of the DispatcherServlet itself, excluding the contextPath and any servletMapping prefix, if present.

The servletPath and pathInfo are decoded and that makes them impossible to compare directly to the full requestURI in order to derive the lookupPath and that makes it necessary to decode the requestURI. However this introduces its own issues because the path may contain encoded reserved characters such as "/" or ";" that can in turn alter the structure of the path after they are decoded which can also lead to security issues. In addition, Servlet containers may normalize the servletPath to varying degrees which makes it further impossible to perform startsWith comparisons against the requestURI.

This is why it is best to avoid reliance on the servletPath which comes with the prefix-based servletPath mapping type. If the DispatcherServlet is mapped as the default Servlet with "/" or otherwise without a prefix with "/*" and the Servlet container is 4.0+ then Spring MVC is able to detect the Servlet mapping type and avoid use of the servletPath and pathInfo altogether. On a 3.1 Servlet container, assuming the same Servlet mapping types, the equivalent can be achieved by providing a UrlPathHelper with alwaysUseFullPath=true via Path Matching in the MVC config.

Fortunately the default Servlet mapping "/" is a good choice. However, there is still an issue in that the requestURI needs to be decoded to make it possible to compare to controller mappings. This is again undesirable because of the potential to decode reserved characters that alter the path structure. If such characters are not expected, then you can reject them (like the Spring Security HTTP firewall), or you can configure UrlPathHelper with urlDecode=false but controller mappings will need to match to the encoded path which may not always work well. Furthermore, sometimes the DispatcherServlet needs to share the URL space with another Servlet and may need to be mapped by prefix.

The above issues can be addressed more comprehensively by switching from PathMatcher to the parsed PathPattern available in 5.3 or higher, see Pattern Comparison. Unlike AntPathMatcher which needs either the lookup path decoded or the controller mapping encoded, a parsed PathPattern matches to a parsed representation of the path called RequestPath, one path segment at a time. This allows decoding and sanitizing path segment values individually without the risk of altering the structure of the path. Parsed PathPattern also supports the use of servletPath prefix mapping as long as the prefix is kept simple and does not have any characters that need to be encoded.

Interception

All HandlerMapping implementations support handler interceptors that are useful when you want to apply specific functionality to certain requests — for example, checking for a principal. Interceptors must implement HandlerInterceptor from the org.springframework.web.servlet package with three methods that should provide enough flexibility to do all kinds of pre-processing and post-processing:

• preHandle(..): Before the actual handler is run

• postHandle(..): After the handler is run

• afterCompletion(..): After the complete request has finished

The preHandle(..) method returns a boolean value. You can use this method to break or continue the processing of the execution chain. When this method returns true, the handler execution chain continues. When it returns false, the DispatcherServlet assumes the interceptor itself has taken care of requests (and, for example, rendered an appropriate view) and does not continue executing the other interceptors and the actual handler in the execution chain.

See Interceptors in the section on MVC configuration for examples of how to configure interceptors. You can also register them directly by using setters on individual HandlerMapping implementations.

postHandle method is less useful with @ResponseBody and ResponseEntity methods for which the response is written and committed within the HandlerAdapter and before postHandle. That means it is too late to make any changes to the response, such as adding an extra header. For such scenarios, you can implement ResponseBodyAdvice and either declare it as an Controller Advice bean or configure it directly on RequestMappingHandlerAdapter.

Exceptions

WebFlux

If an exception occurs during request mapping or is thrown from a request handler (such as a @Controller), the DispatcherServlet delegates to a chain of HandlerExceptionResolver beans to resolve the exception and provide alternative handling, which is typically an error response.

The following table lists the available HandlerExceptionResolver implementations:

Table 2. HandlerExceptionResolver implementations

HandlerExceptionResolver	Description
SimpleMappingExceptionResolver	A mapping between exception class names and error view names. Useful for rendering error pages in a browser application.
{api-spring-framework}/web/servlet/mvc/support/DefaultHandlerExceptionResolver.html[DefaultHandlerExceptionResolver]	Resolves exceptions raised by Spring MVC and maps them to HTTP status codes. See also alternative ResponseEntityExceptionHandler and REST API exceptions.
ResponseStatusExceptionResolver	Resolves exceptions with the @ResponseStatus annotation and maps them to HTTP status codes based on the value in the annotation.
ExceptionHandlerExceptionResolver	Resolves exceptions by invoking an @ExceptionHandler method in a @Controller or a @ControllerAdvice class. See @ExceptionHandler methods.

Chain of Resolvers

You can form an exception resolver chain by declaring multiple HandlerExceptionResolver beans in your Spring configuration and setting their order properties as needed. The higher the order property, the later the exception resolver is positioned.

The contract of HandlerExceptionResolver specifies that it can return:

• a ModelAndView that points to an error view.

• An empty ModelAndView if the exception was handled within the resolver.

• null if the exception remains unresolved, for subsequent resolvers to try, and, if the exception remains at the end, it is allowed to bubble up to the Servlet container.

The MVC Config automatically declares built-in resolvers for default Spring MVC exceptions, for @ResponseStatus annotated exceptions, and for support of @ExceptionHandler methods. You can customize that list or replace it.

Container Error Page

If an exception remains unresolved by any HandlerExceptionResolver and is, therefore, left to propagate or if the response status is set to an error status (that is, 4xx, 5xx), Servlet containers can render a default error page in HTML. To customize the default error page of the container, you can declare an error page mapping in web.xml. The following example shows how to do so:

<error-page>
	<location>/error</location>
</error-page>

Given the preceding example, when an exception bubbles up or the response has an error status, the Servlet container makes an ERROR dispatch within the container to the configured URL (for example, /error). This is then processed by the DispatcherServlet, possibly mapping it to a @Controller, which could be implemented to return an error view name with a model or to render a JSON response, as the following example shows:

Java

@RestController
public class ErrorController {

	@RequestMapping(path = "/error")
	public Map<String, Object> handle(HttpServletRequest request) {
		Map<String, Object> map = new HashMap<String, Object>();
		map.put("status", request.getAttribute("javax.servlet.error.status_code"));
		map.put("reason", request.getAttribute("javax.servlet.error.message"));
		return map;
	}
}

Kotlin

@RestController
class ErrorController {

	@RequestMapping(path = ["/error"])
	fun handle(request: HttpServletRequest): Map<String, Any> {
		val map = HashMap<String, Any>()
		map["status"] = request.getAttribute("javax.servlet.error.status_code")
		map["reason"] = request.getAttribute("javax.servlet.error.message")
		return map
	}
}

Tip	The Servlet API does not provide a way to create error page mappings in Java. You can, however, use both a WebApplicationInitializer and a minimal web.xml.

View Resolution

WebFlux

Spring MVC defines the ViewResolver and View interfaces that let you render models in a browser without tying you to a specific view technology. ViewResolver provides a mapping between view names and actual views. View addresses the preparation of data before handing over to a specific view technology.

The following table provides more details on the ViewResolver hierarchy:

Table 3. ViewResolver implementations

ViewResolver	Description
AbstractCachingViewResolver	Subclasses of AbstractCachingViewResolver cache view instances that they resolve. Caching improves performance of certain view technologies. You can turn off the cache by setting the cache property to false. Furthermore, if you must refresh a certain view at runtime (for example, when a FreeMarker template is modified), you can use the removeFromCache(String viewName, Locale loc) method.
UrlBasedViewResolver	Simple implementation of the ViewResolver interface that effects the direct resolution of logical view names to URLs without an explicit mapping definition. This is appropriate if your logical names match the names of your view resources in a straightforward manner, without the need for arbitrary mappings.
InternalResourceViewResolver	Convenient subclass of UrlBasedViewResolver that supports InternalResourceView (in effect, Servlets and JSPs) and subclasses such as JstlView and TilesView. You can specify the view class for all views generated by this resolver by using setViewClass(..). See the {api-spring-framework}/web/reactive/result/view/UrlBasedViewResolver.html[UrlBasedViewResolver] javadoc for details.
FreeMarkerViewResolver	Convenient subclass of UrlBasedViewResolver that supports FreeMarkerView and custom subclasses of them.
ContentNegotiatingViewResolver	Implementation of the ViewResolver interface that resolves a view based on the request file name or Accept header. See Content Negotiation.
BeanNameViewResolver	Implementation of the ViewResolver interface that interprets a view name as a bean name in the current application context. This is a very flexible variant which allows for mixing and matching different view types based on distinct view names. Each such View can be defined as a bean e.g. in XML or in configuration classes.

Handling

WebFlux

You can chain view resolvers by declaring more than one resolver bean and, if necessary, by setting the order property to specify ordering. Remember, the higher the order property, the later the view resolver is positioned in the chain.

The contract of a ViewResolver specifies that it can return null to indicate that the view could not be found. However, in the case of JSPs and InternalResourceViewResolver, the only way to figure out if a JSP exists is to perform a dispatch through RequestDispatcher. Therefore, you must always configure an InternalResourceViewResolver to be last in the overall order of view resolvers.

Configuring view resolution is as simple as adding ViewResolver beans to your Spring configuration. The MVC Config provides a dedicated configuration API for View Resolvers and for adding logic-less View Controllers which are useful for HTML template rendering without controller logic.

Redirecting

WebFlux

The special redirect: prefix in a view name lets you perform a redirect. The UrlBasedViewResolver (and its subclasses) recognize this as an instruction that a redirect is needed. The rest of the view name is the redirect URL.

The net effect is the same as if the controller had returned a RedirectView, but now the controller itself can operate in terms of logical view names. A logical view name (such as redirect:/myapp/some/resource) redirects relative to the current Servlet context, while a name such as redirect:https://myhost.com/some/arbitrary/path redirects to an absolute URL.

Note that, if a controller method is annotated with the @ResponseStatus, the annotation value takes precedence over the response status set by RedirectView.

Forwarding

You can also use a special forward: prefix for view names that are ultimately resolved by UrlBasedViewResolver and subclasses. This creates an InternalResourceView, which does a RequestDispatcher.forward(). Therefore, this prefix is not useful with InternalResourceViewResolver and InternalResourceView (for JSPs), but it can be helpful if you use another view technology but still want to force a forward of a resource to be handled by the Servlet/JSP engine. Note that you may also chain multiple view resolvers, instead.

Content Negotiation

WebFlux

{api-spring-framework}/web/servlet/view/ContentNegotiatingViewResolver.html[ContentNegotiatingViewResolver] does not resolve views itself but rather delegates to other view resolvers and selects the view that resembles the representation requested by the client. The representation can be determined from the Accept header or from a query parameter (for example, "/path?format=pdf").

The ContentNegotiatingViewResolver selects an appropriate View to handle the request by comparing the request media types with the media type (also known as Content-Type) supported by the View associated with each of its ViewResolvers. The first View in the list that has a compatible Content-Type returns the representation to the client. If a compatible view cannot be supplied by the ViewResolver chain, the list of views specified through the DefaultViews property is consulted. This latter option is appropriate for singleton Views that can render an appropriate representation of the current resource regardless of the logical view name. The Accept header can include wildcards (for example text/*), in which case a View whose Content-Type is text/xml is a compatible match.

See View Resolvers under MVC Config for configuration details.

Locale

Most parts of Spring’s architecture support internationalization, as the Spring web MVC framework does. DispatcherServlet lets you automatically resolve messages by using the client’s locale. This is done with LocaleResolver objects.

When a request comes in, the DispatcherServlet looks for a locale resolver and, if it finds one, it tries to use it to set the locale. By using the RequestContext.getLocale() method, you can always retrieve the locale that was resolved by the locale resolver.

In addition to automatic locale resolution, you can also attach an interceptor to the handler mapping (see Interception for more information on handler mapping interceptors) to change the locale under specific circumstances (for example, based on a parameter in the request).

Locale resolvers and interceptors are defined in the org.springframework.web.servlet.i18n package and are configured in your application context in the normal way. The following selection of locale resolvers is included in Spring.

• Time Zone

• Header Resolver

• Cookie Resolver

• Session Resolver

• Locale Interceptor

Time Zone

In addition to obtaining the client’s locale, it is often useful to know its time zone. The LocaleContextResolver interface offers an extension to LocaleResolver that lets resolvers provide a richer LocaleContext, which may include time zone information.

When available, the user’s TimeZone can be obtained by using the RequestContext.getTimeZone() method. Time zone information is automatically used by any Date/Time Converter and Formatter objects that are registered with Spring’s ConversionService.

Header Resolver

This locale resolver inspects the accept-language header in the request that was sent by the client (for example, a web browser). Usually, this header field contains the locale of the client’s operating system. Note that this resolver does not support time zone information.

Cookie Resolver

This locale resolver inspects a Cookie that might exist on the client to see if a Locale or TimeZone is specified. If so, it uses the specified details. By using the properties of this locale resolver, you can specify the name of the cookie as well as the maximum age. The following example defines a CookieLocaleResolver:

<bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver">

	<property name="cookieName" value="clientlanguage"/>

	<!-- in seconds. If set to -1, the cookie is not persisted (deleted when browser shuts down) -->
	<property name="cookieMaxAge" value="100000"/>

</bean>

The following table describes the properties CookieLocaleResolver:

Table 4. CookieLocaleResolver properties

Property	Default	Description
cookieName	classname + LOCALE	The name of the cookie
cookieMaxAge	Servlet container default	The maximum time a cookie persists on the client. If -1 is specified, the cookie will not be persisted. It is available only until the client shuts down the browser.
cookiePath	/	Limits the visibility of the cookie to a certain part of your site. When cookiePath is specified, the cookie is visible only to that path and the paths below it.

Session Resolver

The SessionLocaleResolver lets you retrieve Locale and TimeZone from the session that might be associated with the user’s request. In contrast to CookieLocaleResolver, this strategy stores locally chosen locale settings in the Servlet container’s HttpSession. As a consequence, those settings are temporary for each session and are, therefore, lost when each session ends.

Note that there is no direct relationship with external session management mechanisms, such as the Spring Session project. This SessionLocaleResolver evaluates and modifies the corresponding HttpSession attributes against the current HttpServletRequest.

Locale Interceptor

You can enable changing of locales by adding the LocaleChangeInterceptor to one of the HandlerMapping definitions. It detects a parameter in the request and changes the locale accordingly, calling the setLocale method on the LocaleResolver in the dispatcher’s application context. The next example shows that calls to all *.view resources that contain a parameter named siteLanguage now changes the locale. So, for example, a request for the URL, https://www.sf.net/home.view?siteLanguage=nl, changes the site language to Dutch. The following example shows how to intercept the locale:

<bean id="localeChangeInterceptor"
		class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor">
	<property name="paramName" value="siteLanguage"/>
</bean>

<bean id="localeResolver"
		class="org.springframework.web.servlet.i18n.CookieLocaleResolver"/>

<bean id="urlMapping"
		class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
	<property name="interceptors">
		<list>
			<ref bean="localeChangeInterceptor"/>
		</list>
	</property>
	<property name="mappings">
		<value>/**/*.view=someController</value>
	</property>
</bean>

Themes

You can apply Spring Web MVC framework themes to set the overall look-and-feel of your application, thereby enhancing user experience. A theme is a collection of static resources, typically style sheets and images, that affect the visual style of the application.

Defining a theme

To use themes in your web application, you must set up an implementation of the org.springframework.ui.context.ThemeSource interface. The WebApplicationContext interface extends ThemeSource but delegates its responsibilities to a dedicated implementation. By default, the delegate is an org.springframework.ui.context.support.ResourceBundleThemeSource implementation that loads properties files from the root of the classpath. To use a custom ThemeSource implementation or to configure the base name prefix of the ResourceBundleThemeSource, you can register a bean in the application context with the reserved name, themeSource. The web application context automatically detects a bean with that name and uses it.

When you use the ResourceBundleThemeSource, a theme is defined in a simple properties file. The properties file lists the resources that make up the theme, as the following example shows:

styleSheet=/themes/cool/style.css
background=/themes/cool/img/coolBg.jpg

The keys of the properties are the names that refer to the themed elements from view code. For a JSP, you typically do this using the spring:theme custom tag, which is very similar to the spring:message tag. The following JSP fragment uses the theme defined in the previous example to customize the look and feel:

<%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%>
<html>
	<head>
		<link rel="stylesheet" href="<spring:theme code='styleSheet'/>" type="text/css"/>
	</head>
	<body style="background=<spring:theme code='background'/>">
		...
	</body>
</html>

By default, the ResourceBundleThemeSource uses an empty base name prefix. As a result, the properties files are loaded from the root of the classpath. Thus, you would put the cool.properties theme definition in a directory at the root of the classpath (for example, in /WEB-INF/classes). The ResourceBundleThemeSource uses the standard Java resource bundle loading mechanism, allowing for full internationalization of themes. For example, we could have a /WEB-INF/classes/cool_nl.properties that references a special background image with Dutch text on it.

Resolving Themes

After you define themes, as described in the preceding section, you decide which theme to use. The DispatcherServlet looks for a bean named themeResolver to find out which ThemeResolver implementation to use. A theme resolver works in much the same way as a LocaleResolver. It detects the theme to use for a particular request and can also alter the request’s theme. The following table describes the theme resolvers provided by Spring:

Table 5. ThemeResolver implementations

Class	Description
FixedThemeResolver	Selects a fixed theme, set by using the defaultThemeName property.
SessionThemeResolver	The theme is maintained in the user’s HTTP session. It needs to be set only once for each session but is not persisted between sessions.
CookieThemeResolver	The selected theme is stored in a cookie on the client.

Spring also provides a ThemeChangeInterceptor that lets theme changes on every request with a simple request parameter.

Multipart Resolver

WebFlux

MultipartResolver from the org.springframework.web.multipart package is a strategy for parsing multipart requests including file uploads. There is one implementation based on Commons FileUpload and another based on Servlet 3.0 multipart request parsing.

To enable multipart handling, you need to declare a MultipartResolver bean in your DispatcherServlet Spring configuration with a name of multipartResolver. The DispatcherServlet detects it and applies it to the incoming request. When a POST with a content type of multipart/form-data is received, the resolver parses the content wraps the current HttpServletRequest as a MultipartHttpServletRequest to provide access to resolved files in addition to exposing parts as request parameters.

Apache Commons FileUpload

To use Apache Commons FileUpload, you can configure a bean of type CommonsMultipartResolver with a name of multipartResolver. You also need to have the commons-fileupload jar as a dependency on your classpath.

This resolver variant delegates to a local library within the application, providing maximum portability across Servlet containers. As an alternative, consider standard Servlet multipart resolution through the container’s own parser as discussed below.

Note	Commons FileUpload traditionally applies to POST requests only but accepts any multipart/ content type. See the {api-spring-framework}/web/multipart/commons/CommonsMultipartResolver.html[CommonsMultipartResolver] javadoc for details and configuration options.

Servlet 3.0

Servlet 3.0 multipart parsing needs to be enabled through Servlet container configuration. To do so:

• In Java, set a MultipartConfigElement on the Servlet registration.

• In web.xml, add a "<multipart-config>" section to the servlet declaration.

The following example shows how to set a MultipartConfigElement on the Servlet registration:

Java

public class AppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {

	// ...

	@Override
	protected void customizeRegistration(ServletRegistration.Dynamic registration) {

		// Optionally also set maxFileSize, maxRequestSize, fileSizeThreshold
		registration.setMultipartConfig(new MultipartConfigElement("/tmp"));
	}

}

Kotlin

class AppInitializer : AbstractAnnotationConfigDispatcherServletInitializer() {

	// ...

	override fun customizeRegistration(registration: ServletRegistration.Dynamic) {

		// Optionally also set maxFileSize, maxRequestSize, fileSizeThreshold
		registration.setMultipartConfig(MultipartConfigElement("/tmp"))
	}

}

Once the Servlet 3.0 configuration is in place, you can add a bean of type StandardServletMultipartResolver with a name of multipartResolver.

Note

This resolver variant uses your Servlet container’s multipart parser as-is, potentially exposing the application to container implementation differences. By default, it will try to parse any multipart/ content type with any HTTP method but this may not be supported across all Servlet containers. See the {api-spring-framework}/web/multipart/support/StandardServletMultipartResolver.html[StandardServletMultipartResolver] javadoc for details and configuration options.

Logging

WebFlux

DEBUG-level logging in Spring MVC is designed to be compact, minimal, and human-friendly. It focuses on high-value bits of information that are useful over and over again versus others that are useful only when debugging a specific issue.

TRACE-level logging generally follows the same principles as DEBUG (and, for example, also should not be a fire hose) but can be used for debugging any issue. In addition, some log messages may show a different level of detail at TRACE versus DEBUG.

Good logging comes from the experience of using the logs. If you spot anything that does not meet the stated goals, please let us know.

Sensitive Data

WebFlux

DEBUG and TRACE logging may log sensitive information. This is why request parameters and headers are masked by default and their logging in full must be enabled explicitly through the enableLoggingRequestDetails property on DispatcherServlet.

The following example shows how to do so by using Java configuration:

Java

public class MyInitializer
		extends AbstractAnnotationConfigDispatcherServletInitializer {

	@Override
	protected Class<?>[] getRootConfigClasses() {
		return ... ;
	}

	@Override
	protected Class<?>[] getServletConfigClasses() {
		return ... ;
	}

	@Override
	protected String[] getServletMappings() {
		return ... ;
	}

	@Override
	protected void customizeRegistration(ServletRegistration.Dynamic registration) {
		registration.setInitParameter("enableLoggingRequestDetails", "true");
	}

}

Kotlin

class MyInitializer : AbstractAnnotationConfigDispatcherServletInitializer() {

	override fun getRootConfigClasses(): Array<Class<*>>? {
		return ...
	}

	override fun getServletConfigClasses(): Array<Class<*>>? {
		return ...
	}

	override fun getServletMappings(): Array<String> {
		return ...
	}

	override fun customizeRegistration(registration: ServletRegistration.Dynamic) {
		registration.setInitParameter("enableLoggingRequestDetails", "true")
	}
}

Filters

WebFlux

The spring-web module provides some useful filters:

• Form Data

• Forwarded Headers

• Shallow ETag

• CORS

Form Data

Browsers can submit form data only through HTTP GET or HTTP POST but non-browser clients can also use HTTP PUT, PATCH, and DELETE. The Servlet API requires ServletRequest.getParameter*() methods to support form field access only for HTTP POST.

The spring-web module provides FormContentFilter to intercept HTTP PUT, PATCH, and DELETE requests with a content type of application/x-www-form-urlencoded, read the form data from the body of the request, and wrap the ServletRequest to make the form data available through the ServletRequest.getParameter*() family of methods.

Forwarded Headers

WebFlux

As a request goes through proxies (such as load balancers) the host, port, and scheme may change, and that makes it a challenge to create links that point to the correct host, port, and scheme from a client perspective.

RFC 7239 defines the Forwarded HTTP header that proxies can use to provide information about the original request. There are other non-standard headers, too, including X-Forwarded-Host, X-Forwarded-Port, X-Forwarded-Proto, X-Forwarded-Ssl, and X-Forwarded-Prefix.

ForwardedHeaderFilter is a Servlet filter that modifies the request in order to a) change the host, port, and scheme based on Forwarded headers, and b) to remove those headers to eliminate further impact. The filter relies on wrapping the request, and therefore it must be ordered ahead of other filters, such as RequestContextFilter, that should work with the modified and not the original request.

There are security considerations for forwarded headers since an application cannot know if the headers were added by a proxy, as intended, or by a malicious client. This is why a proxy at the boundary of trust should be configured to remove untrusted Forwarded headers that come from the outside. You can also configure the ForwardedHeaderFilter with removeOnly=true, in which case it removes but does not use the headers.

In order to support asynchronous requests and error dispatches this filter should be mapped with DispatcherType.ASYNC and also DispatcherType.ERROR. If using Spring Framework’s AbstractAnnotationConfigDispatcherServletInitializer (see Servlet Config) all filters are automatically registered for all dispatch types. However if registering the filter via web.xml or in Spring Boot via a FilterRegistrationBean be sure to include DispatcherType.ASYNC and DispatcherType.ERROR in addition to DispatcherType.REQUEST.

Shallow ETag

The ShallowEtagHeaderFilter filter creates a “shallow” ETag by caching the content written to the response and computing an MD5 hash from it. The next time a client sends, it does the same, but it also compares the computed value against the If-None-Match request header and, if the two are equal, returns a 304 (NOT_MODIFIED).

This strategy saves network bandwidth but not CPU, as the full response must be computed for each request. Other strategies at the controller level, described earlier, can avoid the computation. See HTTP Caching.

This filter has a writeWeakETag parameter that configures the filter to write weak ETags similar to the following: W/"02a2d595e6ed9a0b24f027f2b63b134d6" (as defined in RFC 7232 Section 2.3).

In order to support asynchronous requests this filter must be mapped with DispatcherType.ASYNC so that the filter can delay and successfully generate an ETag to the end of the last async dispatch. If using Spring Framework’s AbstractAnnotationConfigDispatcherServletInitializer (see Servlet Config) all filters are automatically registered for all dispatch types. However if registering the filter via web.xml or in Spring Boot via a FilterRegistrationBean be sure to include DispatcherType.ASYNC.

CORS

WebFlux

Spring MVC provides fine-grained support for CORS configuration through annotations on controllers. However, when used with Spring Security, we advise relying on the built-in CorsFilter that must be ordered ahead of Spring Security’s chain of filters.

See the sections on [mvc-cors] and the [mvc-cors-filter] for more details.

Annotated Controllers

WebFlux

Spring MVC provides an annotation-based programming model where @Controller and @RestController components use annotations to express request mappings, request input, exception handling, and more. Annotated controllers have flexible method signatures and do not have to extend base classes nor implement specific interfaces. The following example shows a controller defined by annotations:

Java

@Controller
public class HelloController {

	@GetMapping("/hello")
	public String handle(Model model) {
		model.addAttribute("message", "Hello World!");
		return "index";
	}
}

Kotlin

import org.springframework.ui.set

@Controller
class HelloController {

	@GetMapping("/hello")
	fun handle(model: Model): String {
		model["message"] = "Hello World!"
		return "index"
	}
}

In the preceding example, the method accepts a Model and returns a view name as a String, but many other options exist and are explained later in this chapter.

Tip	Guides and tutorials on spring.io use the annotation-based programming model described in this section.

Declaration

WebFlux

You can define controller beans by using a standard Spring bean definition in the Servlet’s WebApplicationContext. The @Controller stereotype allows for auto-detection, aligned with Spring general support for detecting @Component classes in the classpath and auto-registering bean definitions for them. It also acts as a stereotype for the annotated class, indicating its role as a web component.

To enable auto-detection of such @Controller beans, you can add component scanning to your Java configuration, as the following example shows:

Java

@Configuration
@ComponentScan("org.example.web")
public class WebConfig {

	// ...
}

Kotlin

@Configuration
@ComponentScan("org.example.web")
class WebConfig {

	// ...
}

The following example shows the XML configuration equivalent of the preceding example:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:p="http://www.springframework.org/schema/p"
	xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="
		http://www.springframework.org/schema/beans
		https://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/context
		https://www.springframework.org/schema/context/spring-context.xsd">

	<context:component-scan base-package="org.example.web"/>

	<!-- ... -->

</beans>

@RestController is a composed annotation that is itself meta-annotated with @Controller and @ResponseBody to indicate a controller whose every method inherits the type-level @ResponseBody annotation and, therefore, writes directly to the response body versus view resolution and rendering with an HTML template.

AOP Proxies

In some cases, you may need to decorate a controller with an AOP proxy at runtime. One example is if you choose to have @Transactional annotations directly on the controller. When this is the case, for controllers specifically, we recommend using class-based proxying. This is typically the default choice with controllers. However, if a controller must implement an interface that is not a Spring Context callback (such as InitializingBean, *Aware, and others), you may need to explicitly configure class-based proxying. For example, with <tx:annotation-driven/> you can change to <tx:annotation-driven proxy-target-class="true"/>, and with @EnableTransactionManagement you can change to @EnableTransactionManagement(proxyTargetClass = true).

Request Mapping

WebFlux

You can use the @RequestMapping annotation to map requests to controllers methods. It has various attributes to match by URL, HTTP method, request parameters, headers, and media types. You can use it at the class level to express shared mappings or at the method level to narrow down to a specific endpoint mapping.

There are also HTTP method specific shortcut variants of @RequestMapping:

• @GetMapping

• @PostMapping

• @PutMapping

• @DeleteMapping

• @PatchMapping

The shortcuts are Custom Annotations that are provided because, arguably, most controller methods should be mapped to a specific HTTP method versus using @RequestMapping, which, by default, matches to all HTTP methods. A @RequestMapping is still needed at the class level to express shared mappings.

The following example has type and method level mappings:

Java

@RestController
@RequestMapping("/persons")
class PersonController {

	@GetMapping("/{id}")
	public Person getPerson(@PathVariable Long id) {
		// ...
	}

	@PostMapping
	@ResponseStatus(HttpStatus.CREATED)
	public void add(@RequestBody Person person) {
		// ...
	}
}

Kotlin

@RestController
@RequestMapping("/persons")
class PersonController {

	@GetMapping("/{id}")
	fun getPerson(@PathVariable id: Long): Person {
		// ...
	}

	@PostMapping
	@ResponseStatus(HttpStatus.CREATED)
	fun add(@RequestBody person: Person) {
		// ...
	}
}

URI patterns

WebFlux

@RequestMapping methods can be mapped using URL patterns. There are two alternatives:

• PathPattern — a pre-parsed pattern matched against the URL path also pre-parsed as PathContainer. Designed for web use, this solution deals effectively with encoding and path parameters, and matches efficiently.

• AntPathMatcher — match String patterns against a String path. This is the original solution also used in Spring configuration to select resources on the classpath, on the filesystem, and other locations. It is less efficient and the String path input is a challenge for dealing effectively with encoding and other issues with URLs.

PathPattern is the recommended solution for web applications and it is the only choice in Spring WebFlux. Prior to version 5.3, AntPathMatcher was the only choice in Spring MVC and continues to be the default. However PathPattern can be enabled in the MVC config.

PathPattern supports the same pattern syntax as AntPathMatcher. In addition it also supports the capturing pattern, e.g. {*spring}, for matching 0 or more path segments at the end of a path. PathPattern also restricts the use of ** for matching multiple path segments such that it’s only allowed at the end of a pattern. This eliminates many cases of ambiguity when choosing the best matching pattern for a given request. For full pattern syntax please refer to {api-spring-framework}/web/util/pattern/PathPattern.html[PathPattern] and {api-spring-framework}/util/AntPathMatcher.html[AntPathMatcher].

Some example patterns:

• "/resources/ima?e.png" - match one character in a path segment

• "/resources/*.png" - match zero or more characters in a path segment

• "/resources/**" - match multiple path segments

• "/projects/{project}/versions" - match a path segment and capture it as a variable

• "/projects/{project:[a-z]}/versions"+ - match and capture a variable with a regex

Captured URI variables can be accessed with @PathVariable. For example:

Java

@GetMapping("/owners/{ownerId}/pets/{petId}")
public Pet findPet(@PathVariable Long ownerId, @PathVariable Long petId) {
	// ...
}

Kotlin

@GetMapping("/owners/{ownerId}/pets/{petId}")
fun findPet(@PathVariable ownerId: Long, @PathVariable petId: Long): Pet {
	// ...
}

You can declare URI variables at the class and method levels, as the following example shows:

Java

@Controller
@RequestMapping("/owners/{ownerId}")
public class OwnerController {

	@GetMapping("/pets/{petId}")
	public Pet findPet(@PathVariable Long ownerId, @PathVariable Long petId) {
		// ...
	}
}

Kotlin

@Controller
@RequestMapping("/owners/{ownerId}")
class OwnerController {

	@GetMapping("/pets/{petId}")
	fun findPet(@PathVariable ownerId: Long, @PathVariable petId: Long): Pet {
		// ...
	}
}

URI variables are automatically converted to the appropriate type, or TypeMismatchException is raised. Simple types (int, long, Date, and so on) are supported by default and you can register support for any other data type. See Type Conversion and DataBinder.

You can explicitly name URI variables (for example, @PathVariable("customId")), but you can leave that detail out if the names are the same and your code is compiled with debugging information or with the -parameters compiler flag on Java 8.

The syntax {varName:regex} declares a URI variable with a regular expression that has syntax of {varName:regex}. For example, given URL "/spring-web-3.0.5.jar", the following method extracts the name, version, and file extension:

Java

@GetMapping("/{name:[a-z-]+}-{version:\\d\\.\\d\\.\\d}{ext:\\.[a-z]+}")
public void handle(@PathVariable String name, @PathVariable String version, @PathVariable String ext) {
	// ...
}

Kotlin

@GetMapping("/{name:[a-z-]+}-{version:\\d\\.\\d\\.\\d}{ext:\\.[a-z]+}")
fun handle(@PathVariable name: String, @PathVariable version: String, @PathVariable ext: String) {
	// ...
}

URI path patterns can also have embedded ${…​} placeholders that are resolved on startup by using PropertySourcesPlaceholderConfigurer against local, system, environment, and other property sources. You can use this, for example, to parameterize a base URL based on some external configuration.

Pattern Comparison

WebFlux

When multiple patterns match a URL, the best match must be selected. This is done with one of the following depending on whether use of parsed PathPattern is enabled for use or not:

• {api-spring-framework}/web/util/pattern/PathPattern.html#SPECIFICITY_COMPARATOR[PathPattern.SPECIFICITY_COMPARATOR]

• {api-spring-framework}/util/AntPathMatcher.html#getPatternComparator-java.lang.String-[AntPathMatcher.getPatternComparator(String path)]

Both help to sort patterns with more specific ones on top. A pattern is less specific if it has a lower count of URI variables (counted as 1), single wildcards (counted as 1), and double wildcards (counted as 2). Given an equal score, the longer pattern is chosen. Given the same score and length, the pattern with more URI variables than wildcards is chosen.

The default mapping pattern (/**) is excluded from scoring and always sorted last. Also, prefix patterns (such as /public/**) are considered less specific than other pattern that do not have double wildcards.

For the full details, follow the above links to the pattern Comparators.

Suffix Match

Starting in 5.3, by default Spring MVC no longer performs .* suffix pattern matching where a controller mapped to /person is also implicitly mapped to /person.*. As a consequence path extensions are no longer used to interpret the requested content type for the response — for example, /person.pdf, /person.xml, and so on.

Using file extensions in this way was necessary when browsers used to send Accept headers that were hard to interpret consistently. At present, that is no longer a necessity and using the Accept header should be the preferred choice.

Over time, the use of file name extensions has proven problematic in a variety of ways. It can cause ambiguity when overlain with the use of URI variables, path parameters, and URI encoding. Reasoning about URL-based authorization and security (see next section for more details) also becomes more difficult.

To completely disable the use of path extensions in versions prior to 5.3, set the following:

• useSuffixPatternMatching(false), see PathMatchConfigurer

• favorPathExtension(false), see ContentNegotiationConfigurer

Having a way to request content types other than through the "Accept" header can still be useful, e.g. when typing a URL in a browser. A safe alternative to path extensions is to use the query parameter strategy. If you must use file extensions, consider restricting them to a list of explicitly registered extensions through the mediaTypes property of ContentNegotiationConfigurer.

Suffix Match and RFD

A reflected file download (RFD) attack is similar to XSS in that it relies on request input (for example, a query parameter and a URI variable) being reflected in the response. However, instead of inserting JavaScript into HTML, an RFD attack relies on the browser switching to perform a download and treating the response as an executable script when double-clicked later.

In Spring MVC, @ResponseBody and ResponseEntity methods are at risk, because they can render different content types, which clients can request through URL path extensions. Disabling suffix pattern matching and using path extensions for content negotiation lower the risk but are not sufficient to prevent RFD attacks.

To prevent RFD attacks, prior to rendering the response body, Spring MVC adds a Content-Disposition:inline;filename=f.txt header to suggest a fixed and safe download file. This is done only if the URL path contains a file extension that is neither allowed as safe nor explicitly registered for content negotiation. However, it can potentially have side effects when URLs are typed directly into a browser.

Many common path extensions are allowed as safe by default. Applications with custom HttpMessageConverter implementations can explicitly register file extensions for content negotiation to avoid having a Content-Disposition header added for those extensions. See Content Types.

See CVE-2015-5211 for additional recommendations related to RFD.

Consumable Media Types

WebFlux

You can narrow the request mapping based on the Content-Type of the request, as the following example shows:

Java

@PostMapping(path = "/pets", consumes = "application/json") // (1)
public void addPet(@RequestBody Pet pet) {
	// ...
}

1. Using a consumes attribute to narrow the mapping by the content type.

Kotlin

@PostMapping("/pets", consumes = ["application/json"]) // (1)
fun addPet(@RequestBody pet: Pet) {
	// ...
}

1. Using a consumes attribute to narrow the mapping by the content type.

The consumes attribute also supports negation expressions — for example, !text/plain means any content type other than text/plain.

You can declare a shared consumes attribute at the class level. Unlike most other request-mapping attributes, however, when used at the class level, a method-level consumes attribute overrides rather than extends the class-level declaration.

Tip	MediaType provides constants for commonly used media types, such as APPLICATION_JSON_VALUE and APPLICATION_XML_VALUE.

Producible Media Types

WebFlux

You can narrow the request mapping based on the Accept request header and the list of content types that a controller method produces, as the following example shows:

Java

@GetMapping(path = "/pets/{petId}", produces = "application/json") // (1)
@ResponseBody
public Pet getPet(@PathVariable String petId) {
	// ...
}

1. Using a produces attribute to narrow the mapping by the content type.

Kotlin

@GetMapping("/pets/{petId}", produces = ["application/json"]) // (1)
@ResponseBody
fun getPet(@PathVariable petId: String): Pet {
	// ...
}

1. Using a produces attribute to narrow the mapping by the content type.

The media type can specify a character set. Negated expressions are supported — for example, !text/plain means any content type other than "text/plain".

You can declare a shared produces attribute at the class level. Unlike most other request-mapping attributes, however, when used at the class level, a method-level produces attribute overrides rather than extends the class-level declaration.

Tip	MediaType provides constants for commonly used media types, such as APPLICATION_JSON_VALUE and APPLICATION_XML_VALUE.

Parameters, headers

WebFlux

You can narrow request mappings based on request parameter conditions. You can test for the presence of a request parameter (myParam), for the absence of one (!myParam), or for a specific value (myParam=myValue). The following example shows how to test for a specific value:

Java

@GetMapping(path = "/pets/{petId}", params = "myParam=myValue") // (1)
public void findPet(@PathVariable String petId) {
	// ...
}

1. Testing whether myParam equals myValue.

Kotlin

@GetMapping("/pets/{petId}", params = ["myParam=myValue"]) // (1)
fun findPet(@PathVariable petId: String) {
	// ...
}

1. Testing whether myParam equals myValue.

You can also use the same with request header conditions, as the following example shows:

Java

@GetMapping(path = "/pets", headers = "myHeader=myValue") // (1)
public void findPet(@PathVariable String petId) {
	// ...
}

1. Testing whether myHeader equals myValue.

Kotlin

@GetMapping("/pets", headers = ["myHeader=myValue"]) // (1)
fun findPet(@PathVariable petId: String) {
	// ...
}

Tip	You can match Content-Type and Accept with the headers condition, but it is better to use consumes and produces instead.

HTTP HEAD, OPTIONS

WebFlux

@GetMapping (and @RequestMapping(method=HttpMethod.GET)) support HTTP HEAD transparently for request mapping. Controller methods do not need to change. A response wrapper, applied in javax.servlet.http.HttpServlet, ensures a Content-Length header is set to the number of bytes written (without actually writing to the response).

@GetMapping (and @RequestMapping(method=HttpMethod.GET)) are implicitly mapped to and support HTTP HEAD. An HTTP HEAD request is processed as if it were HTTP GET except that, instead of writing the body, the number of bytes are counted and the Content-Length header is set.

By default, HTTP OPTIONS is handled by setting the Allow response header to the list of HTTP methods listed in all @RequestMapping methods that have matching URL patterns.

For a @RequestMapping without HTTP method declarations, the Allow header is set to GET,HEAD,POST,PUT,PATCH,DELETE,OPTIONS. Controller methods should always declare the supported HTTP methods (for example, by using the HTTP method specific variants: @GetMapping, @PostMapping, and others).

You can explicitly map the @RequestMapping method to HTTP HEAD and HTTP OPTIONS, but that is not necessary in the common case.

Custom Annotations

WebFlux

Spring MVC supports the use of composed annotations for request mapping. Those are annotations that are themselves meta-annotated with @RequestMapping and composed to redeclare a subset (or all) of the @RequestMapping attributes with a narrower, more specific purpose.

@GetMapping, @PostMapping, @PutMapping, @DeleteMapping, and @PatchMapping are examples of composed annotations. They are provided because, arguably, most controller methods should be mapped to a specific HTTP method versus using @RequestMapping, which, by default, matches to all HTTP methods. If you need an example of composed annotations, look at how those are declared.

Spring MVC also supports custom request-mapping attributes with custom request-matching logic. This is a more advanced option that requires subclassing RequestMappingHandlerMapping and overriding the getCustomMethodCondition method, where you can check the custom attribute and return your own RequestCondition.

Explicit Registrations

WebFlux

You can programmatically register handler methods, which you can use for dynamic registrations or for advanced cases, such as different instances of the same handler under different URLs. The following example registers a handler method:

Java

@Configuration
public class MyConfig {

	@Autowired
	public void setHandlerMapping(RequestMappingHandlerMapping mapping, UserHandler handler) // (1)
			throws NoSuchMethodException {

		RequestMappingInfo info = RequestMappingInfo
				.paths("/user/{id}").methods(RequestMethod.GET).build(); // (2)

		Method method = UserHandler.class.getMethod("getUser", Long.class); // (3)

		mapping.registerMapping(info, handler, method); // (4)
	}
}

1. Inject the target handler and the handler mapping for controllers.

2. Prepare the request mapping meta data.

3. Get the handler method.

4. Add the registration.

Kotlin

@Configuration
class MyConfig {

	@Autowired
	fun setHandlerMapping(mapping: RequestMappingHandlerMapping, handler: UserHandler) { // (1)
		val info = RequestMappingInfo.paths("/user/{id}").methods(RequestMethod.GET).build() // (2)
		val method = UserHandler::class.java.getMethod("getUser", Long::class.java) // (3)
		mapping.registerMapping(info, handler, method) // (4)
	}
}

1. Inject the target handler and the handler mapping for controllers.

2. Prepare the request mapping meta data.

3. Get the handler method.

4. Add the registration.

Handler Methods

WebFlux

@RequestMapping handler methods have a flexible signature and can choose from a range of supported controller method arguments and return values.

Method Arguments

WebFlux

The next table describes the supported controller method arguments. Reactive types are not supported for any arguments.

JDK 8’s java.util.Optional is supported as a method argument in combination with annotations that have a required attribute (for example, @RequestParam, @RequestHeader, and others) and is equivalent to required=false.

Controller method argument	Description
WebRequest, NativeWebRequest	Generic access to request parameters and request and session attributes, without direct use of the Servlet API.
javax.servlet.ServletRequest, javax.servlet.ServletResponse	Choose any specific request or response type — for example, ServletRequest, HttpServletRequest, or Spring’s MultipartRequest, MultipartHttpServletRequest.
javax.servlet.http.HttpSession	Enforces the presence of a session. As a consequence, such an argument is never null. Note that session access is not thread-safe. Consider setting the RequestMappingHandlerAdapter instance’s synchronizeOnSession flag to true if multiple requests are allowed to concurrently access a session.
javax.servlet.http.PushBuilder	Servlet 4.0 push builder API for programmatic HTTP/2 resource pushes. Note that, per the Servlet specification, the injected PushBuilder instance can be null if the client does not support that HTTP/2 feature.
java.security.Principal	Currently authenticated user — possibly a specific Principal implementation class if known. Note that this argument is not resolved eagerly, if it is annotated in order to allow a custom resolver to resolve it before falling back on default resolution via HttpServletRequest#getUserPrincipal. For example, the Spring Security Authentication implements Principal and would be injected as such via HttpServletRequest#getUserPrincipal, unless it is also annotated with @AuthenticationPrincipal in which case it is resolved by a custom Spring Security resolver through Authentication#getPrincipal.
HttpMethod	The HTTP method of the request.
java.util.Locale	The current request locale, determined by the most specific LocaleResolver available (in effect, the configured LocaleResolver or LocaleContextResolver).
java.util.TimeZone + java.time.ZoneId	The time zone associated with the current request, as determined by a LocaleContextResolver.
java.io.InputStream, java.io.Reader	For access to the raw request body as exposed by the Servlet API.
java.io.OutputStream, java.io.Writer	For access to the raw response body as exposed by the Servlet API.
@PathVariable	For access to URI template variables. See URI patterns.
@MatrixVariable	For access to name-value pairs in URI path segments. See Matrix Variables.
@RequestParam	For access to the Servlet request parameters, including multipart files. Parameter values are converted to the declared method argument type. See @RequestParam as well as Multipart. Note that use of @RequestParam is optional for simple parameter values. See “Any other argument”, at the end of this table.
@RequestHeader	For access to request headers. Header values are converted to the declared method argument type. See @RequestHeader.
@CookieValue	For access to cookies. Cookies values are converted to the declared method argument type. See @CookieValue.
@RequestBody	For access to the HTTP request body. Body content is converted to the declared method argument type by using HttpMessageConverter implementations. See @RequestBody.
HttpEntity<B>	For access to request headers and body. The body is converted with an HttpMessageConverter. See HttpEntity.
@RequestPart	For access to a part in a multipart/form-data request, converting the part’s body with an HttpMessageConverter. See Multipart.
java.util.Map, org.springframework.ui.Model, org.springframework.ui.ModelMap	For access to the model that is used in HTML controllers and exposed to templates as part of view rendering.
RedirectAttributes	Specify attributes to use in case of a redirect (that is, to be appended to the query string) and flash attributes to be stored temporarily until the request after redirect. See Redirect Attributes and Flash Attributes.
@ModelAttribute	For access to an existing attribute in the model (instantiated if not present) with data binding and validation applied. See @ModelAttribute as well as Model and DataBinder. Note that use of @ModelAttribute is optional (for example, to set its attributes). See “Any other argument” at the end of this table.
Errors, BindingResult	For access to errors from validation and data binding for a command object (that is, a @ModelAttribute argument) or errors from the validation of a @RequestBody or @RequestPart arguments. You must declare an Errors, or BindingResult argument immediately after the validated method argument.
SessionStatus + class-level @SessionAttributes	For marking form processing complete, which triggers cleanup of session attributes declared through a class-level @SessionAttributes annotation. See @SessionAttributes for more details.
UriComponentsBuilder	For preparing a URL relative to the current request’s host, port, scheme, context path, and the literal part of the servlet mapping. See URI Links.
@SessionAttribute	For access to any session attribute, in contrast to model attributes stored in the session as a result of a class-level @SessionAttributes declaration. See @SessionAttribute for more details.
@RequestAttribute	For access to request attributes. See @RequestAttribute for more details.
Any other argument	If a method argument is not matched to any of the earlier values in this table and it is a simple type (as determined by {api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty]), it is resolved as a @RequestParam. Otherwise, it is resolved as a @ModelAttribute.

Return Values

WebFlux

The next table describes the supported controller method return values. Reactive types are supported for all return values.

Controller method return value	Description
@ResponseBody	The return value is converted through HttpMessageConverter implementations and written to the response. See @ResponseBody.
HttpEntity<B>, ResponseEntity<B>	The return value that specifies the full response (including HTTP headers and body) is to be converted through HttpMessageConverter implementations and written to the response. See ResponseEntity.
HttpHeaders	For returning a response with headers and no body.
String	A view name to be resolved with ViewResolver implementations and used together with the implicit model — determined through command objects and @ModelAttribute methods. The handler method can also programmatically enrich the model by declaring a Model argument (see Explicit Registrations).
View	A View instance to use for rendering together with the implicit model — determined through command objects and @ModelAttribute methods. The handler method can also programmatically enrich the model by declaring a Model argument (see Explicit Registrations).
java.util.Map, org.springframework.ui.Model	Attributes to be added to the implicit model, with the view name implicitly determined through a RequestToViewNameTranslator.
@ModelAttribute	An attribute to be added to the model, with the view name implicitly determined through a RequestToViewNameTranslator. Note that @ModelAttribute is optional. See "Any other return value" at the end of this table.
ModelAndView object	The view and model attributes to use and, optionally, a response status.
void	A method with a void return type (or null return value) is considered to have fully handled the response if it also has a ServletResponse, an OutputStream argument, or an @ResponseStatus annotation. The same is also true if the controller has made a positive ETag or lastModified timestamp check (see Controllers for details). If none of the above is true, a void return type can also indicate “no response body” for REST controllers or a default view name selection for HTML controllers.
DeferredResult<V>	Produce any of the preceding return values asynchronously from any thread — for example, as a result of some event or callback. See Asynchronous Requests and DeferredResult.
Callable<V>	Produce any of the above return values asynchronously in a Spring MVC-managed thread. See Asynchronous Requests and Callable.
ListenableFuture<V>, java.util.concurrent.CompletionStage<V>, java.util.concurrent.CompletableFuture<V>	Alternative to DeferredResult, as a convenience (for example, when an underlying service returns one of those).
ResponseBodyEmitter, SseEmitter	Emit a stream of objects asynchronously to be written to the response with HttpMessageConverter implementations. Also supported as the body of a ResponseEntity. See Asynchronous Requests and HTTP Streaming.
StreamingResponseBody	Write to the response OutputStream asynchronously. Also supported as the body of a ResponseEntity. See Asynchronous Requests and HTTP Streaming.
Reactor and other reactive types registered via ReactiveAdapterRegistry	A single value type, e.g. Mono, is comparable to returning DeferredResult. A multi-value type, e.g. Flux, may be treated as a stream depending on the requested media type, e.g. "text/event-stream", "application/json+stream", or otherwise is collected to a List and rendered as a single value. See Asynchronous Requests and Reactive Types.
Other return values	If a return value remains unresolved in any other way, it is treated as a model attribute, unless it is a simple type as determined by {api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty], in which case it remains unresolved.

Type Conversion

WebFlux

Some annotated controller method arguments that represent String-based request input (such as @RequestParam, @RequestHeader, @PathVariable, @MatrixVariable, and @CookieValue) can require type conversion if the argument is declared as something other than String.

For such cases, type conversion is automatically applied based on the configured converters. By default, simple types (int, long, Date, and others) are supported. You can customize type conversion through a WebDataBinder (see DataBinder) or by registering Formatters with the FormattingConversionService. See Spring Field Formatting.

A practical issue in type conversion is the treatment of an empty String source value. Such a value is treated as missing if it becomes null as a result of type conversion. This can be the case for Long, UUID, and other target types. If you want to allow null to be injected, either use the required flag on the argument annotation, or declare the argument as @Nullable.

Note

As of 5.3, non-null arguments will be enforced even after type conversion. If your handler method intends to accept a null value as well, either declare your argument as @Nullable or mark it as required=false in the corresponding @RequestParam, etc. annotation. This is a best practice and the recommended solution for regressions encountered in a 5.3 upgrade. Alternatively, you may specifically handle e.g. the resulting MissingPathVariableException in the case of a required @PathVariable. A null value after conversion will be treated like an empty original value, so the corresponding Missing…​Exception variants will be thrown.

Matrix Variables

WebFlux

RFC 3986 discusses name-value pairs in path segments. In Spring MVC, we refer to those as “matrix variables” based on an “old post” by Tim Berners-Lee, but they can be also be referred to as URI path parameters.

Matrix variables can appear in any path segment, with each variable separated by a semicolon and multiple values separated by comma (for example, /cars;color=red,green;year=2012). Multiple values can also be specified through repeated variable names (for example, color=red;color=green;color=blue).

If a URL is expected to contain matrix variables, the request mapping for a controller method must use a URI variable to mask that variable content and ensure the request can be matched successfully independent of matrix variable order and presence. The following example uses a matrix variable:

Java

// GET /pets/42;q=11;r=22

@GetMapping("/pets/{petId}")
public void findPet(@PathVariable String petId, @MatrixVariable int q) {

	// petId == 42
	// q == 11
}

Kotlin

// GET /pets/42;q=11;r=22

@GetMapping("/pets/{petId}")
fun findPet(@PathVariable petId: String, @MatrixVariable q: Int) {

	// petId == 42
	// q == 11
}

Given that all path segments may contain matrix variables, you may sometimes need to disambiguate which path variable the matrix variable is expected to be in. The following example shows how to do so:

Java

// GET /owners/42;q=11/pets/21;q=22

@GetMapping("/owners/{ownerId}/pets/{petId}")
public void findPet(
		@MatrixVariable(name="q", pathVar="ownerId") int q1,
		@MatrixVariable(name="q", pathVar="petId") int q2) {

	// q1 == 11
	// q2 == 22
}

Kotlin

// GET /owners/42;q=11/pets/21;q=22

@GetMapping("/owners/{ownerId}/pets/{petId}")
fun findPet(
		@MatrixVariable(name = "q", pathVar = "ownerId") q1: Int,
		@MatrixVariable(name = "q", pathVar = "petId") q2: Int) {

	// q1 == 11
	// q2 == 22
}

A matrix variable may be defined as optional and a default value specified, as the following example shows:

Java

// GET /pets/42

@GetMapping("/pets/{petId}")
public void findPet(@MatrixVariable(required=false, defaultValue="1") int q) {

	// q == 1
}

Kotlin

// GET /pets/42

@GetMapping("/pets/{petId}")
fun findPet(@MatrixVariable(required = false, defaultValue = "1") q: Int) {

	// q == 1
}

To get all matrix variables, you can use a MultiValueMap, as the following example shows:

Java

// GET /owners/42;q=11;r=12/pets/21;q=22;s=23

@GetMapping("/owners/{ownerId}/pets/{petId}")
public void findPet(
		@MatrixVariable MultiValueMap<String, String> matrixVars,
		@MatrixVariable(pathVar="petId") MultiValueMap<String, String> petMatrixVars) {

	// matrixVars: ["q" : [11,22], "r" : 12, "s" : 23]
	// petMatrixVars: ["q" : 22, "s" : 23]
}

Kotlin

// GET /owners/42;q=11;r=12/pets/21;q=22;s=23

@GetMapping("/owners/{ownerId}/pets/{petId}")
fun findPet(
		@MatrixVariable matrixVars: MultiValueMap<String, String>,
		@MatrixVariable(pathVar="petId") petMatrixVars: MultiValueMap<String, String>) {

	// matrixVars: ["q" : [11,22], "r" : 12, "s" : 23]
	// petMatrixVars: ["q" : 22, "s" : 23]
}

Note that you need to enable the use of matrix variables. In the MVC Java configuration, you need to set a UrlPathHelper with removeSemicolonContent=false through Path Matching. In the MVC XML namespace, you can set <mvc:annotation-driven enable-matrix-variables="true"/>.

@RequestParam

WebFlux

You can use the @RequestParam annotation to bind Servlet request parameters (that is, query parameters or form data) to a method argument in a controller.

The following example shows how to do so:

Java

@Controller
@RequestMapping("/pets")
public class EditPetForm {

	// ...

	@GetMapping
	public String setupForm(@RequestParam("petId") int petId, Model model) { (1)
		Pet pet = this.clinic.loadPet(petId);
		model.addAttribute("pet", pet);
		return "petForm";
	}

	// ...

}

1. Using @RequestParam to bind petId.

Kotlin

import org.springframework.ui.set

@Controller
@RequestMapping("/pets")
class EditPetForm {

	// ...

	@GetMapping
	fun setupForm(@RequestParam("petId") petId: Int, model: Model): String { // (1)
		val pet = this.clinic.loadPet(petId);
		model["pet"] = pet
		return "petForm"
	}

	// ...

}

1. Using @RequestParam to bind petId.

By default, method parameters that use this annotation are required, but you can specify that a method parameter is optional by setting the @RequestParam annotation’s required flag to false or by declaring the argument with an java.util.Optional wrapper.

Type conversion is automatically applied if the target method parameter type is not String. See Type Conversion.

Declaring the argument type as an array or list allows for resolving multiple parameter values for the same parameter name.

When an @RequestParam annotation is declared as a Map<String, String> or MultiValueMap<String, String>, without a parameter name specified in the annotation, then the map is populated with the request parameter values for each given parameter name.

Note that use of @RequestParam is optional (for example, to set its attributes). By default, any argument that is a simple value type (as determined by {api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty]) and is not resolved by any other argument resolver, is treated as if it were annotated with @RequestParam.

@RequestHeader

WebFlux

You can use the @RequestHeader annotation to bind a request header to a method argument in a controller.

Consider the following request, with headers:

Host                    localhost:8080
Accept                  text/html,application/xhtml+xml,application/xml;q=0.9
Accept-Language         fr,en-gb;q=0.7,en;q=0.3
Accept-Encoding         gzip,deflate
Accept-Charset          ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive              300

The following example gets the value of the Accept-Encoding and Keep-Alive headers:

Java

@GetMapping("/demo")
public void handle(
		@RequestHeader("Accept-Encoding") String encoding, // (1)
		@RequestHeader("Keep-Alive") long keepAlive) { // (2)
	//...
}

1. Get the value of the Accept-Encoding header.

2. Get the value of the Keep-Alive header.

Kotlin

@GetMapping("/demo")
fun handle(
		@RequestHeader("Accept-Encoding") encoding: String, // (1)
		@RequestHeader("Keep-Alive") keepAlive: Long) { // (2)
	//...
}

1. Get the value of the Accept-Encoding header.

2. Get the value of the Keep-Alive header.

If the target method parameter type is not String, type conversion is automatically applied. See Type Conversion.

When an @RequestHeader annotation is used on a Map<String, String>, MultiValueMap<String, String>, or HttpHeaders argument, the map is populated with all header values.

Tip	Built-in support is available for converting a comma-separated string into an array or collection of strings or other types known to the type conversion system. For example, a method parameter annotated with @RequestHeader("Accept") can be of type String but also String[] or List<String>.

@CookieValue

WebFlux

You can use the @CookieValue annotation to bind the value of an HTTP cookie to a method argument in a controller.

Consider a request with the following cookie:

JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84

The following example shows how to get the cookie value:

Java

@GetMapping("/demo")
public void handle(@CookieValue("JSESSIONID") String cookie) { (1)
	//...
}

1. Get the value of the JSESSIONID cookie.

Kotlin

@GetMapping("/demo")
fun handle(@CookieValue("JSESSIONID") cookie: String) { // (1)
	//...
}

1. Get the value of the JSESSIONID cookie.

If the target method parameter type is not String, type conversion is applied automatically. See Type Conversion.

@ModelAttribute

WebFlux

You can use the @ModelAttribute annotation on a method argument to access an attribute from the model or have it be instantiated if not present. The model attribute is also overlain with values from HTTP Servlet request parameters whose names match to field names. This is referred to as data binding, and it saves you from having to deal with parsing and converting individual query parameters and form fields. The following example shows how to do so:

Java

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@ModelAttribute Pet pet) {
	// method logic...
}

Kotlin

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
fun processSubmit(@ModelAttribute pet: Pet): String {
	// method logic...
}

The Pet instance above is sourced in one of the following ways:

• Retrieved from the model where it may have been added by a @ModelAttribute method.

• Retrieved from the HTTP session if the model attribute was listed in the class-level @SessionAttributes annotation.

• Obtained through a Converter where the model attribute name matches the name of a request value such as a path variable or a request parameter (see next example).

• Instantiated using its default constructor.

• Instantiated through a “primary constructor” with arguments that match to Servlet request parameters. Argument names are determined through JavaBeans @ConstructorProperties or through runtime-retained parameter names in the bytecode.

One alternative to using a @ModelAttribute method to supply it or relying on the framework to create the model attribute, is to have a Converter<String, T> to provide the instance. This is applied when the model attribute name matches to the name of a request value such as a path variable or a request parameter, and there is a Converter from String to the model attribute type. In the following example, the model attribute name is account which matches the URI path variable account, and there is a registered Converter<String, Account> which could load the Account from a data store:

Java

@PutMapping("/accounts/{account}")
public String save(@ModelAttribute("account") Account account) {
	// ...
}

Kotlin

@PutMapping("/accounts/{account}")
fun save(@ModelAttribute("account") account: Account): String {
	// ...
}

After the model attribute instance is obtained, data binding is applied. The WebDataBinder class matches Servlet request parameter names (query parameters and form fields) to field names on the target Object. Matching fields are populated after type conversion is applied, where necessary. For more on data binding (and validation), see Validation. For more on customizing data binding, see DataBinder.

Data binding can result in errors. By default, a BindException is raised. However, to check for such errors in the controller method, you can add a BindingResult argument immediately next to the @ModelAttribute, as the following example shows:

Java

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) { // (1)
	if (result.hasErrors()) {
		return "petForm";
	}
	// ...
}

1. Adding a BindingResult next to the @ModelAttribute.

Kotlin

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
fun processSubmit(@ModelAttribute("pet") pet: Pet, result: BindingResult): String { // (1)
	if (result.hasErrors()) {
		return "petForm"
	}
	// ...
}

1. Adding a BindingResult next to the @ModelAttribute.

In some cases, you may want access to a model attribute without data binding. For such cases, you can inject the Model into the controller and access it directly or, alternatively, set @ModelAttribute(binding=false), as the following example shows:

Java

@ModelAttribute
public AccountForm setUpForm() {
	return new AccountForm();
}

@ModelAttribute
public Account findAccount(@PathVariable String accountId) {
	return accountRepository.findOne(accountId);
}

@PostMapping("update")
public String update(@Valid AccountForm form, BindingResult result,
		@ModelAttribute(binding=false) Account account) { // (1)
	// ...
}

1. Setting @ModelAttribute(binding=false).

Kotlin

@ModelAttribute
fun setUpForm(): AccountForm {
	return AccountForm()
}

@ModelAttribute
fun findAccount(@PathVariable accountId: String): Account {
	return accountRepository.findOne(accountId)
}

@PostMapping("update")
fun update(@Valid form: AccountForm, result: BindingResult,
		   @ModelAttribute(binding = false) account: Account): String { // (1)
	// ...
}

1. Setting @ModelAttribute(binding=false).

You can automatically apply validation after data binding by adding the javax.validation.Valid annotation or Spring’s @Validated annotation (Bean Validation and Spring validation). The following example shows how to do so:

Java

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@Valid @ModelAttribute("pet") Pet pet, BindingResult result) { // (1)
	if (result.hasErrors()) {
		return "petForm";
	}
	// ...
}

1. Validate the Pet instance.

Kotlin

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
fun processSubmit(@Valid @ModelAttribute("pet") pet: Pet, result: BindingResult): String { // (1)
	if (result.hasErrors()) {
		return "petForm"
	}
	// ...
}

Note that using @ModelAttribute is optional (for example, to set its attributes). By default, any argument that is not a simple value type (as determined by {api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty]) and is not resolved by any other argument resolver is treated as if it were annotated with @ModelAttribute.

@SessionAttributes

WebFlux

@SessionAttributes is used to store model attributes in the HTTP Servlet session between requests. It is a type-level annotation that declares the session attributes used by a specific controller. This typically lists the names of model attributes or types of model attributes that should be transparently stored in the session for subsequent requests to access.

The following example uses the @SessionAttributes annotation:

Java

@Controller
@SessionAttributes("pet") // (1)
public class EditPetForm {
	// ...
}

1. Using the @SessionAttributes annotation.

Kotlin

@Controller
@SessionAttributes("pet") // (1)
class EditPetForm {
	// ...
}

1. Using the @SessionAttributes annotation.

On the first request, when a model attribute with the name, pet, is added to the model, it is automatically promoted to and saved in the HTTP Servlet session. It remains there until another controller method uses a SessionStatus method argument to clear the storage, as the following example shows:

Java

@Controller
@SessionAttributes("pet") // (1)
public class EditPetForm {

	// ...

	@PostMapping("/pets/{id}")
	public String handle(Pet pet, BindingResult errors, SessionStatus status) {
		if (errors.hasErrors) {
			// ...
		}
		status.setComplete(); // (2)
		// ...
	}
}

1. Storing the Pet value in the Servlet session.

2. Clearing the Pet value from the Servlet session.

Kotlin

@Controller
@SessionAttributes("pet") // (1)
class EditPetForm {

	// ...

	@PostMapping("/pets/{id}")
	fun handle(pet: Pet, errors: BindingResult, status: SessionStatus): String {
		if (errors.hasErrors()) {
			// ...
		}
		status.setComplete() // (2)
		// ...
	}
}

1. Storing the Pet value in the Servlet session.

2. Clearing the Pet value from the Servlet session.

@SessionAttribute

WebFlux

If you need access to pre-existing session attributes that are managed globally (that is, outside the controller — for example, by a filter) and may or may not be present, you can use the @SessionAttribute annotation on a method parameter, as the following example shows:

Java

@RequestMapping("/")
public String handle(@SessionAttribute User user) { (1)
	// ...
}

1. Using a @SessionAttribute annotation.

Kotlin

@RequestMapping("/")
fun handle(@SessionAttribute user: User): String { // (1)
	// ...
}

For use cases that require adding or removing session attributes, consider injecting org.springframework.web.context.request.WebRequest or javax.servlet.http.HttpSession into the controller method.

For temporary storage of model attributes in the session as part of a controller workflow, consider using @SessionAttributes as described in @SessionAttributes.

@RequestAttribute

WebFlux

Similar to @SessionAttribute, you can use the @RequestAttribute annotations to access pre-existing request attributes created earlier (for example, by a Servlet Filter or HandlerInterceptor):

Java

@GetMapping("/")
public String handle(@RequestAttribute Client client) { // (1)
	// ...
}

1. Using the @RequestAttribute annotation.

Kotlin

@GetMapping("/")
fun handle(@RequestAttribute client: Client): String { // (1)
	// ...
}

1. Using the @RequestAttribute annotation.

Redirect Attributes

By default, all model attributes are considered to be exposed as URI template variables in the redirect URL. Of the remaining attributes, those that are primitive types or collections or arrays of primitive types are automatically appended as query parameters.

Appending primitive type attributes as query parameters can be the desired result if a model instance was prepared specifically for the redirect. However, in annotated controllers, the model can contain additional attributes added for rendering purposes (for example, drop-down field values). To avoid the possibility of having such attributes appear in the URL, a @RequestMapping method can declare an argument of type RedirectAttributes and use it to specify the exact attributes to make available to RedirectView. If the method does redirect, the content of RedirectAttributes is used. Otherwise, the content of the model is used.

The RequestMappingHandlerAdapter provides a flag called ignoreDefaultModelOnRedirect, which you can use to indicate that the content of the default Model should never be used if a controller method redirects. Instead, the controller method should declare an attribute of type RedirectAttributes or, if it does not do so, no attributes should be passed on to RedirectView. Both the MVC namespace and the MVC Java configuration keep this flag set to false, to maintain backwards compatibility. However, for new applications, we recommend setting it to true.

Note that URI template variables from the present request are automatically made available when expanding a redirect URL, and you don’t need to explicitly add them through Model or RedirectAttributes. The following example shows how to define a redirect:

Java

@PostMapping("/files/{path}")
public String upload(...) {
	// ...
	return "redirect:files/{path}";
}

Kotlin

@PostMapping("/files/{path}")
fun upload(...): String {
	// ...
	return "redirect:files/{path}"
}

Another way of passing data to the redirect target is by using flash attributes. Unlike other redirect attributes, flash attributes are saved in the HTTP session (and, hence, do not appear in the URL). See Flash Attributes for more information.

Flash Attributes

Flash attributes provide a way for one request to store attributes that are intended for use in another. This is most commonly needed when redirecting — for example, the Post-Redirect-Get pattern. Flash attributes are saved temporarily before the redirect (typically in the session) to be made available to the request after the redirect and are removed immediately.

Spring MVC has two main abstractions in support of flash attributes. FlashMap is used to hold flash attributes, while FlashMapManager is used to store, retrieve, and manage FlashMap instances.

Flash attribute support is always “on” and does not need to be enabled explicitly. However, if not used, it never causes HTTP session creation. On each request, there is an “input” FlashMap with attributes passed from a previous request (if any) and an “output” FlashMap with attributes to save for a subsequent request. Both FlashMap instances are accessible from anywhere in Spring MVC through static methods in RequestContextUtils.

Annotated controllers typically do not need to work with FlashMap directly. Instead, a @RequestMapping method can accept an argument of type RedirectAttributes and use it to add flash attributes for a redirect scenario. Flash attributes added through RedirectAttributes are automatically propagated to the “output” FlashMap. Similarly, after the redirect, attributes from the “input” FlashMap are automatically added to the Model of the controller that serves the target URL.

Matching requests to flash attributes

The concept of flash attributes exists in many other web frameworks and has proven to sometimes be exposed to concurrency issues. This is because, by definition, flash attributes are to be stored until the next request. However the very “next” request may not be the intended recipient but another asynchronous request (for example, polling or resource requests), in which case the flash attributes are removed too early.

To reduce the possibility of such issues, RedirectView automatically “stamps” FlashMap instances with the path and query parameters of the target redirect URL. In turn, the default FlashMapManager matches that information to incoming requests when it looks up the “input” FlashMap.

This does not entirely eliminate the possibility of a concurrency issue but reduces it greatly with information that is already available in the redirect URL. Therefore, we recommend that you use flash attributes mainly for redirect scenarios.

Multipart

WebFlux

After a MultipartResolver has been enabled, the content of POST requests with multipart/form-data is parsed and accessible as regular request parameters. The following example accesses one regular form field and one uploaded file:

Java

@Controller
public class FileUploadController {

	@PostMapping("/form")
	public String handleFormUpload(@RequestParam("name") String name,
			@RequestParam("file") MultipartFile file) {

		if (!file.isEmpty()) {
			byte[] bytes = file.getBytes();
			// store the bytes somewhere
			return "redirect:uploadSuccess";
		}
		return "redirect:uploadFailure";
	}
}

Kotlin

@Controller
class FileUploadController {

	@PostMapping("/form")
	fun handleFormUpload(@RequestParam("name") name: String,
						@RequestParam("file") file: MultipartFile): String {

		if (!file.isEmpty) {
			val bytes = file.bytes
			// store the bytes somewhere
			return "redirect:uploadSuccess"
		}
		return "redirect:uploadFailure"
	}
}

Declaring the argument type as a List<MultipartFile> allows for resolving multiple files for the same parameter name.

When the @RequestParam annotation is declared as a Map<String, MultipartFile> or MultiValueMap<String, MultipartFile>, without a parameter name specified in the annotation, then the map is populated with the multipart files for each given parameter name.

Note	With Servlet 3.0 multipart parsing, you may also declare javax.servlet.http.Part instead of Spring’s MultipartFile, as a method argument or collection value type.

You can also use multipart content as part of data binding to a command object. For example, the form field and file from the preceding example could be fields on a form object, as the following example shows:

Java

class MyForm {

	private String name;

	private MultipartFile file;

	// ...
}

@Controller
public class FileUploadController {

	@PostMapping("/form")
	public String handleFormUpload(MyForm form, BindingResult errors) {
		if (!form.getFile().isEmpty()) {
			byte[] bytes = form.getFile().getBytes();
			// store the bytes somewhere
			return "redirect:uploadSuccess";
		}
		return "redirect:uploadFailure";
	}
}

Kotlin

class MyForm(val name: String, val file: MultipartFile, ...)

@Controller
class FileUploadController {

	@PostMapping("/form")
	fun handleFormUpload(form: MyForm, errors: BindingResult): String {
		if (!form.file.isEmpty) {
			val bytes = form.file.bytes
			// store the bytes somewhere
			return "redirect:uploadSuccess"
		}
		return "redirect:uploadFailure"
	}
}

Multipart requests can also be submitted from non-browser clients in a RESTful service scenario. The following example shows a file with JSON:

POST /someUrl
Content-Type: multipart/mixed

--edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp
Content-Disposition: form-data; name="meta-data"
Content-Type: application/json; charset=UTF-8
Content-Transfer-Encoding: 8bit

{
	"name": "value"
}
--edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp
Content-Disposition: form-data; name="file-data"; filename="file.properties"
Content-Type: text/xml
Content-Transfer-Encoding: 8bit
... File Data ...

You can access the "meta-data" part with @RequestParam as a String but you’ll probably want it deserialized from JSON (similar to @RequestBody). Use the @RequestPart annotation to access a multipart after converting it with an HttpMessageConverter:

Java

@PostMapping("/")
public String handle(@RequestPart("meta-data") MetaData metadata,
		@RequestPart("file-data") MultipartFile file) {
	// ...
}

Kotlin

@PostMapping("/")
fun handle(@RequestPart("meta-data") metadata: MetaData,
		@RequestPart("file-data") file: MultipartFile): String {
	// ...
}

You can use @RequestPart in combination with javax.validation.Valid or use Spring’s @Validated annotation, both of which cause Standard Bean Validation to be applied. By default, validation errors cause a MethodArgumentNotValidException, which is turned into a 400 (BAD_REQUEST) response. Alternatively, you can handle validation errors locally within the controller through an Errors or BindingResult argument, as the following example shows:

Java

@PostMapping("/")
public String handle(@Valid @RequestPart("meta-data") MetaData metadata,
		BindingResult result) {
	// ...
}

Kotlin

@PostMapping("/")
fun handle(@Valid @RequestPart("meta-data") metadata: MetaData,
		result: BindingResult): String {
	// ...
}

@RequestBody

WebFlux

You can use the @RequestBody annotation to have the request body read and deserialized into an Object through an HttpMessageConverter. The following example uses a @RequestBody argument:

Java

@PostMapping("/accounts")
public void handle(@RequestBody Account account) {
	// ...
}

Kotlin

@PostMapping("/accounts")
fun handle(@RequestBody account: Account) {
	// ...
}

You can use the Message Converters option of the MVC Config to configure or customize message conversion.

You can use @RequestBody in combination with javax.validation.Valid or Spring’s @Validated annotation, both of which cause Standard Bean Validation to be applied. By default, validation errors cause a MethodArgumentNotValidException, which is turned into a 400 (BAD_REQUEST) response. Alternatively, you can handle validation errors locally within the controller through an Errors or BindingResult argument, as the following example shows:

Java

@PostMapping("/accounts")
public void handle(@Valid @RequestBody Account account, BindingResult result) {
	// ...
}

Kotlin

@PostMapping("/accounts")
fun handle(@Valid @RequestBody account: Account, result: BindingResult) {
	// ...
}

HttpEntity

WebFlux

HttpEntity is more or less identical to using @RequestBody but is based on a container object that exposes request headers and body. The following listing shows an example:

Java

@PostMapping("/accounts")
public void handle(HttpEntity<Account> entity) {
	// ...
}

Kotlin

@PostMapping("/accounts")
fun handle(entity: HttpEntity<Account>) {
	// ...
}

@ResponseBody

WebFlux

You can use the @ResponseBody annotation on a method to have the return serialized to the response body through an HttpMessageConverter. The following listing shows an example:

Java

@GetMapping("/accounts/{id}")
@ResponseBody
public Account handle() {
	// ...
}

Kotlin

@GetMapping("/accounts/{id}")
@ResponseBody
fun handle(): Account {
	// ...
}

@ResponseBody is also supported at the class level, in which case it is inherited by all controller methods. This is the effect of @RestController, which is nothing more than a meta-annotation marked with @Controller and @ResponseBody.

You can use @ResponseBody with reactive types. See Asynchronous Requests and Reactive Types for more details.

You can use the Message Converters option of the MVC Config to configure or customize message conversion.

You can combine @ResponseBody methods with JSON serialization views. See Jackson JSON for details.

ResponseEntity

WebFlux

ResponseEntity is like @ResponseBody but with status and headers. For example:

Java

@GetMapping("/something")
public ResponseEntity<String> handle() {
	String body = ... ;
	String etag = ... ;
	return ResponseEntity.ok().eTag(etag).body(body);
}

Kotlin

@GetMapping("/something")
fun handle(): ResponseEntity<String> {
	val body = ...
	val etag = ...
	return ResponseEntity.ok().eTag(etag).build(body)
}

Spring MVC supports using a single value reactive type to produce the ResponseEntity asynchronously, and/or single and multi-value reactive types for the body. This allows the following types of async responses:

• ResponseEntity<Mono<T>> or ResponseEntity<Flux<T>> make the response status and headers known immediately while the body is provided asynchronously at a later point. Use Mono if the body consists of 0..1 values or Flux if it can produce multiple values.

• Mono<ResponseEntity<T>> provides all three — response status, headers, and body, asynchronously at a later point. This allows the response status and headers to vary depending on the outcome of asynchronous request handling.

Jackson JSON

Spring offers support for the Jackson JSON library.

JSON Views

WebFlux

Spring MVC provides built-in support for Jackson’s Serialization Views, which allow rendering only a subset of all fields in an Object. To use it with @ResponseBody or ResponseEntity controller methods, you can use Jackson’s @JsonView annotation to activate a serialization view class, as the following example shows:

Java

@RestController
public class UserController {

	@GetMapping("/user")
	@JsonView(User.WithoutPasswordView.class)
	public User getUser() {
		return new User("eric", "7!jd#h23");
	}
}

public class User {

	public interface WithoutPasswordView {};
	public interface WithPasswordView extends WithoutPasswordView {};

	private String username;
	private String password;

	public User() {
	}

	public User(String username, String password) {
		this.username = username;
		this.password = password;
	}

	@JsonView(WithoutPasswordView.class)
	public String getUsername() {
		return this.username;
	}

	@JsonView(WithPasswordView.class)
	public String getPassword() {
		return this.password;
	}
}

Kotlin

@RestController
class UserController {

	@GetMapping("/user")
	@JsonView(User.WithoutPasswordView::class)
	fun getUser() = User("eric", "7!jd#h23")
}

class User(
		@JsonView(WithoutPasswordView::class) val username: String,
		@JsonView(WithPasswordView::class) val password: String) {

	interface WithoutPasswordView
	interface WithPasswordView : WithoutPasswordView
}

Note	@JsonView allows an array of view classes, but you can specify only one per controller method. If you need to activate multiple views, you can use a composite interface.

If you want to do the above programmatically, instead of declaring an @JsonView annotation, wrap the return value with MappingJacksonValue and use it to supply the serialization view:

Java

@RestController
public class UserController {

	@GetMapping("/user")
	public MappingJacksonValue getUser() {
		User user = new User("eric", "7!jd#h23");
		MappingJacksonValue value = new MappingJacksonValue(user);
		value.setSerializationView(User.WithoutPasswordView.class);
		return value;
	}
}

Kotlin

@RestController
class UserController {

	@GetMapping("/user")
	fun getUser(): MappingJacksonValue {
		val value = MappingJacksonValue(User("eric", "7!jd#h23"))
		value.serializationView = User.WithoutPasswordView::class.java
		return value
	}
}

For controllers that rely on view resolution, you can add the serialization view class to the model, as the following example shows:

Java

@Controller
public class UserController extends AbstractController {

	@GetMapping("/user")
	public String getUser(Model model) {
		model.addAttribute("user", new User("eric", "7!jd#h23"));
		model.addAttribute(JsonView.class.getName(), User.WithoutPasswordView.class);
		return "userView";
	}
}

Kotlin

import org.springframework.ui.set

@Controller
class UserController : AbstractController() {

	@GetMapping("/user")
	fun getUser(model: Model): String {
		model["user"] = User("eric", "7!jd#h23")
		model[JsonView::class.qualifiedName] = User.WithoutPasswordView::class.java
		return "userView"
	}
}

Model

WebFlux

You can use the @ModelAttribute annotation:

• On a method argument in @RequestMapping methods to create or access an Object from the model and to bind it to the request through a WebDataBinder.

• As a method-level annotation in @Controller or @ControllerAdvice classes that help to initialize the model prior to any @RequestMapping method invocation.

• On a @RequestMapping method to mark its return value is a model attribute.

This section discusses @ModelAttribute methods — the second item in the preceding list. A controller can have any number of @ModelAttribute methods. All such methods are invoked before @RequestMapping methods in the same controller. A @ModelAttribute method can also be shared across controllers through @ControllerAdvice. See the section on Controller Advice for more details.

@ModelAttribute methods have flexible method signatures. They support many of the same arguments as @RequestMapping methods, except for @ModelAttribute itself or anything related to the request body.

The following example shows a @ModelAttribute method:

Java

@ModelAttribute
public void populateModel(@RequestParam String number, Model model) {
	model.addAttribute(accountRepository.findAccount(number));
	// add more ...
}

Kotlin

@ModelAttribute
fun populateModel(@RequestParam number: String, model: Model) {
	model.addAttribute(accountRepository.findAccount(number))
	// add more ...
}

The following example adds only one attribute:

Java

@ModelAttribute
public Account addAccount(@RequestParam String number) {
	return accountRepository.findAccount(number);
}

Kotlin

@ModelAttribute
fun addAccount(@RequestParam number: String): Account {
	return accountRepository.findAccount(number)
}

Note

When a name is not explicitly specified, a default name is chosen based on the Object type, as explained in the javadoc for {api-spring-framework}/core/Conventions.html[Conventions]. You can always assign an explicit name by using the overloaded addAttribute method or through the name attribute on @ModelAttribute (for a return value).

You can also use @ModelAttribute as a method-level annotation on @RequestMapping methods, in which case the return value of the @RequestMapping method is interpreted as a model attribute. This is typically not required, as it is the default behavior in HTML controllers, unless the return value is a String that would otherwise be interpreted as a view name. @ModelAttribute can also customize the model attribute name, as the following example shows:

Java

@GetMapping("/accounts/{id}")
@ModelAttribute("myAccount")
public Account handle() {
	// ...
	return account;
}

Kotlin

@GetMapping("/accounts/{id}")
@ModelAttribute("myAccount")
fun handle(): Account {
	// ...
	return account
}

DataBinder

WebFlux

@Controller or @ControllerAdvice classes can have @InitBinder methods that initialize instances of WebDataBinder, and those, in turn, can:

• Bind request parameters (that is, form or query data) to a model object.

• Convert String-based request values (such as request parameters, path variables, headers, cookies, and others) to the target type of controller method arguments.

• Format model object values as String values when rendering HTML forms.

@InitBinder methods can register controller-specific java.beans.PropertyEditor or Spring Converter and Formatter components. In addition, you can use the MVC config to register Converter and Formatter types in a globally shared FormattingConversionService.

@InitBinder methods support many of the same arguments that @RequestMapping methods do, except for @ModelAttribute (command object) arguments. Typically, they are declared with a WebDataBinder argument (for registrations) and a void return value. The following listing shows an example:

Java

@Controller
public class FormController {

	@InitBinder // (1)
	public void initBinder(WebDataBinder binder) {
		SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
		dateFormat.setLenient(false);
		binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false));
	}

	// ...
}

1. Defining an @InitBinder method.

Kotlin

@Controller
class FormController {

	@InitBinder // (1)
	fun initBinder(binder: WebDataBinder) {
		val dateFormat = SimpleDateFormat("yyyy-MM-dd")
		dateFormat.isLenient = false
		binder.registerCustomEditor(Date::class.java, CustomDateEditor(dateFormat, false))
	}

	// ...
}

1. Defining an @InitBinder method.

Alternatively, when you use a Formatter-based setup through a shared FormattingConversionService, you can re-use the same approach and register controller-specific Formatter implementations, as the following example shows:

Java

@Controller
public class FormController {

	@InitBinder // (1)
	protected void initBinder(WebDataBinder binder) {
		binder.addCustomFormatter(new DateFormatter("yyyy-MM-dd"));
	}

	// ...
}

1. Defining an @InitBinder method on a custom formatter.

Kotlin

@Controller
class FormController {

	@InitBinder // (1)
	protected fun initBinder(binder: WebDataBinder) {
		binder.addCustomFormatter(DateFormatter("yyyy-MM-dd"))
	}

	// ...
}

1. Defining an @InitBinder method on a custom formatter.

Model Design

WebFlux

web-data-binding-model-design.adoc

Exceptions

WebFlux

@Controller and @ControllerAdvice classes can have @ExceptionHandler methods to handle exceptions from controller methods, as the following example shows:

Java

@Controller
public class SimpleController {

	// ...

	@ExceptionHandler
	public ResponseEntity<String> handle(IOException ex) {
		// ...
	}
}

Kotlin

@Controller
class SimpleController {

	// ...

	@ExceptionHandler
	fun handle(ex: IOException): ResponseEntity<String> {
		// ...
	}
}

The exception may match against a top-level exception being propagated (e.g. a direct IOException being thrown) or against a nested cause within a wrapper exception (e.g. an IOException wrapped inside an IllegalStateException). As of 5.3, this can match at arbitrary cause levels, whereas previously only an immediate cause was considered.

For matching exception types, preferably declare the target exception as a method argument, as the preceding example shows. When multiple exception methods match, a root exception match is generally preferred to a cause exception match. More specifically, the ExceptionDepthComparator is used to sort exceptions based on their depth from the thrown exception type.

Alternatively, the annotation declaration may narrow the exception types to match, as the following example shows:

Java

@ExceptionHandler({FileSystemException.class, RemoteException.class})
public ResponseEntity<String> handle(IOException ex) {
	// ...
}

Kotlin

@ExceptionHandler(FileSystemException::class, RemoteException::class)
fun handle(ex: IOException): ResponseEntity<String> {
	// ...
}

You can even use a list of specific exception types with a very generic argument signature, as the following example shows:

Java

@ExceptionHandler({FileSystemException.class, RemoteException.class})
public ResponseEntity<String> handle(Exception ex) {
	// ...
}

Kotlin

@ExceptionHandler(FileSystemException::class, RemoteException::class)
fun handle(ex: Exception): ResponseEntity<String> {
	// ...
}

Note

The distinction between root and cause exception matching can be surprising. In the IOException variant shown earlier, the method is typically called with the actual FileSystemException or RemoteException instance as the argument, since both of them extend from IOException. However, if any such matching exception is propagated within a wrapper exception which is itself an IOException, the passed-in exception instance is that wrapper exception. The behavior is even simpler in the handle(Exception) variant. This is always invoked with the wrapper exception in a wrapping scenario, with the actually matching exception to be found through ex.getCause() in that case. The passed-in exception is the actual FileSystemException or RemoteException instance only when these are thrown as top-level exceptions.

We generally recommend that you be as specific as possible in the argument signature, reducing the potential for mismatches between root and cause exception types. Consider breaking a multi-matching method into individual @ExceptionHandler methods, each matching a single specific exception type through its signature.

In a multi-@ControllerAdvice arrangement, we recommend declaring your primary root exception mappings on a @ControllerAdvice prioritized with a corresponding order. While a root exception match is preferred to a cause, this is defined among the methods of a given controller or @ControllerAdvice class. This means a cause match on a higher-priority @ControllerAdvice bean is preferred to any match (for example, root) on a lower-priority @ControllerAdvice bean.

Last but not least, an @ExceptionHandler method implementation can choose to back out of dealing with a given exception instance by rethrowing it in its original form. This is useful in scenarios where you are interested only in root-level matches or in matches within a specific context that cannot be statically determined. A rethrown exception is propagated through the remaining resolution chain, as though the given @ExceptionHandler method would not have matched in the first place.

Support for @ExceptionHandler methods in Spring MVC is built on the DispatcherServlet level, HandlerExceptionResolver mechanism.

Method Arguments

@ExceptionHandler methods support the following arguments:

Method argument	Description
Exception type	For access to the raised exception.
HandlerMethod	For access to the controller method that raised the exception.
WebRequest, NativeWebRequest	Generic access to request parameters and request and session attributes without direct use of the Servlet API.
javax.servlet.ServletRequest, javax.servlet.ServletResponse	Choose any specific request or response type (for example, ServletRequest or HttpServletRequest or Spring’s MultipartRequest or MultipartHttpServletRequest).
javax.servlet.http.HttpSession	Enforces the presence of a session. As a consequence, such an argument is never null. Note that session access is not thread-safe. Consider setting the RequestMappingHandlerAdapter instance’s synchronizeOnSession flag to true if multiple requests are allowed to access a session concurrently.
java.security.Principal	Currently authenticated user — possibly a specific Principal implementation class if known.
HttpMethod	The HTTP method of the request.
java.util.Locale	The current request locale, determined by the most specific LocaleResolver available — in effect, the configured LocaleResolver or LocaleContextResolver.
java.util.TimeZone, java.time.ZoneId	The time zone associated with the current request, as determined by a LocaleContextResolver.
java.io.OutputStream, java.io.Writer	For access to the raw response body, as exposed by the Servlet API.
java.util.Map, org.springframework.ui.Model, org.springframework.ui.ModelMap	For access to the model for an error response. Always empty.
RedirectAttributes	Specify attributes to use in case of a redirect — (that is to be appended to the query string) and flash attributes to be stored temporarily until the request after the redirect. See Redirect Attributes and Flash Attributes.
@SessionAttribute	For access to any session attribute, in contrast to model attributes stored in the session as a result of a class-level @SessionAttributes declaration. See @SessionAttribute for more details.
@RequestAttribute	For access to request attributes. See @RequestAttribute for more details.

Return Values

@ExceptionHandler methods support the following return values:

Return value	Description
@ResponseBody	The return value is converted through HttpMessageConverter instances and written to the response. See @ResponseBody.
HttpEntity<B>, ResponseEntity<B>	The return value specifies that the full response (including the HTTP headers and the body) be converted through HttpMessageConverter instances and written to the response. See ResponseEntity.
String	A view name to be resolved with ViewResolver implementations and used together with the implicit model — determined through command objects and @ModelAttribute methods. The handler method can also programmatically enrich the model by declaring a Model argument (described earlier).
View	A View instance to use for rendering together with the implicit model — determined through command objects and @ModelAttribute methods. The handler method may also programmatically enrich the model by declaring a Model argument (descried earlier).
java.util.Map, org.springframework.ui.Model	Attributes to be added to the implicit model with the view name implicitly determined through a RequestToViewNameTranslator.
@ModelAttribute	An attribute to be added to the model with the view name implicitly determined through a RequestToViewNameTranslator. Note that @ModelAttribute is optional. See “Any other return value” at the end of this table.
ModelAndView object	The view and model attributes to use and, optionally, a response status.
void	A method with a void return type (or null return value) is considered to have fully handled the response if it also has a ServletResponse an OutputStream argument, or a @ResponseStatus annotation. The same is also true if the controller has made a positive ETag or lastModified timestamp check (see Controllers for details). If none of the above is true, a void return type can also indicate “no response body” for REST controllers or default view name selection for HTML controllers.
Any other return value	If a return value is not matched to any of the above and is not a simple type (as determined by {api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty]), by default, it is treated as a model attribute to be added to the model. If it is a simple type, it remains unresolved.

REST API exceptions

WebFlux

A common requirement for REST services is to include error details in the body of the response. The Spring Framework does not automatically do this because the representation of error details in the response body is application-specific. However, a @RestController may use @ExceptionHandler methods with a ResponseEntity return value to set the status and the body of the response. Such methods can also be declared in @ControllerAdvice classes to apply them globally.

Applications that implement global exception handling with error details in the response body should consider extending {api-spring-framework}/web/servlet/mvc/method/annotation/ResponseEntityExceptionHandler.html[ResponseEntityExceptionHandler], which provides handling for exceptions that Spring MVC raises and provides hooks to customize the response body. To make use of this, create a subclass of ResponseEntityExceptionHandler, annotate it with @ControllerAdvice, override the necessary methods, and declare it as a Spring bean.

Controller Advice

WebFlux

@ExceptionHandler, @InitBinder, and @ModelAttribute methods apply only to the @Controller class, or class hierarchy, in which they are declared. If, instead, they are declared in an @ControllerAdvice or @RestControllerAdvice class, then they apply to any controller. Moreover, as of 5.3, @ExceptionHandler methods in @ControllerAdvice can be used to handle exceptions from any @Controller or any other handler.

@ControllerAdvice is meta-annotated with @Component and therefore can be registered as a Spring bean through component scanning. @RestControllerAdvice is meta-annotated with @ControllerAdvice and @ResponseBody, and that means @ExceptionHandler methods will have their return value rendered via response body message conversion, rather than via HTML views.

On startup, RequestMappingHandlerMapping and ExceptionHandlerExceptionResolver detect controller advice beans and apply them at runtime. Global @ExceptionHandler methods, from an @ControllerAdvice, are applied after local ones, from the @Controller. By contrast, global @ModelAttribute and @InitBinder methods are applied before local ones.

The @ControllerAdvice annotation has attributes that let you narrow the set of controllers and handlers that they apply to. For example:

Java

// Target all Controllers annotated with @RestController
@ControllerAdvice(annotations = RestController.class)
public class ExampleAdvice1 {}

// Target all Controllers within specific packages
@ControllerAdvice("org.example.controllers")
public class ExampleAdvice2 {}

// Target all Controllers assignable to specific classes
@ControllerAdvice(assignableTypes = {ControllerInterface.class, AbstractController.class})
public class ExampleAdvice3 {}

Kotlin

// Target all Controllers annotated with @RestController
@ControllerAdvice(annotations = [RestController::class])
class ExampleAdvice1

// Target all Controllers within specific packages
@ControllerAdvice("org.example.controllers")
class ExampleAdvice2

// Target all Controllers assignable to specific classes
@ControllerAdvice(assignableTypes = [ControllerInterface::class, AbstractController::class])
class ExampleAdvice3

The selectors in the preceding example are evaluated at runtime and may negatively impact performance if used extensively. See the {api-spring-framework}/web/bind/annotation/ControllerAdvice.html[@ControllerAdvice] javadoc for more details.

webmvc-functional.adoc

URI Links

WebFlux

This section describes various options available in the Spring Framework to work with URI’s.

web-uris.adoc

Relative Servlet Requests

You can use ServletUriComponentsBuilder to create URIs relative to the current request, as the following example shows:

Java

HttpServletRequest request = ...

// Re-uses scheme, host, port, path, and query string...

URI uri = ServletUriComponentsBuilder.fromRequest(request)
		.replaceQueryParam("accountId", "{id}")
		.build("123");

Kotlin

val request: HttpServletRequest = ...

// Re-uses scheme, host, port, path, and query string...

val uri = ServletUriComponentsBuilder.fromRequest(request)
		.replaceQueryParam("accountId", "{id}")
		.build("123")

You can create URIs relative to the context path, as the following example shows:

Java

HttpServletRequest request = ...

// Re-uses scheme, host, port, and context path...

URI uri = ServletUriComponentsBuilder.fromContextPath(request)
		.path("/accounts")
		.build()
		.toUri();

Kotlin

val request: HttpServletRequest = ...

// Re-uses scheme, host, port, and context path...

val uri = ServletUriComponentsBuilder.fromContextPath(request)
		.path("/accounts")
		.build()
		.toUri()

You can create URIs relative to a Servlet (for example, /main/*), as the following example shows:

Java

HttpServletRequest request = ...

// Re-uses scheme, host, port, context path, and Servlet mapping prefix...

URI uri = ServletUriComponentsBuilder.fromServletMapping(request)
		.path("/accounts")
		.build()
		.toUri();

Kotlin

val request: HttpServletRequest = ...

// Re-uses scheme, host, port, context path, and Servlet mapping prefix...

val uri = ServletUriComponentsBuilder.fromServletMapping(request)
		.path("/accounts")
		.build()
		.toUri()

Note	As of 5.1, ServletUriComponentsBuilder ignores information from the Forwarded and X-Forwarded-* headers, which specify the client-originated address. Consider using the ForwardedHeaderFilter to extract and use or to discard such headers.

Links to Controllers

Spring MVC provides a mechanism to prepare links to controller methods. For example, the following MVC controller allows for link creation:

Java

@Controller
@RequestMapping("/hotels/{hotel}")
public class BookingController {

	@GetMapping("/bookings/{booking}")
	public ModelAndView getBooking(@PathVariable Long booking) {
		// ...
	}
}

Kotlin

@Controller
@RequestMapping("/hotels/{hotel}")
class BookingController {

	@GetMapping("/bookings/{booking}")
	fun getBooking(@PathVariable booking: Long): ModelAndView {
		// ...
	}
}

You can prepare a link by referring to the method by name, as the following example shows:

Java

UriComponents uriComponents = MvcUriComponentsBuilder
	.fromMethodName(BookingController.class, "getBooking", 21).buildAndExpand(42);

URI uri = uriComponents.encode().toUri();

Kotlin

val uriComponents = MvcUriComponentsBuilder
	.fromMethodName(BookingController::class.java, "getBooking", 21).buildAndExpand(42)

val uri = uriComponents.encode().toUri()

In the preceding example, we provide actual method argument values (in this case, the long value: 21) to be used as a path variable and inserted into the URL. Furthermore, we provide the value, 42, to fill in any remaining URI variables, such as the hotel variable inherited from the type-level request mapping. If the method had more arguments, we could supply null for arguments not needed for the URL. In general, only @PathVariable and @RequestParam arguments are relevant for constructing the URL.

There are additional ways to use MvcUriComponentsBuilder. For example, you can use a technique akin to mock testing through proxies to avoid referring to the controller method by name, as the following example shows (the example assumes static import of MvcUriComponentsBuilder.on):

Java

UriComponents uriComponents = MvcUriComponentsBuilder
	.fromMethodCall(on(BookingController.class).getBooking(21)).buildAndExpand(42);

URI uri = uriComponents.encode().toUri();

Kotlin

val uriComponents = MvcUriComponentsBuilder
	.fromMethodCall(on(BookingController::class.java).getBooking(21)).buildAndExpand(42)

val uri = uriComponents.encode().toUri()

Note

Controller method signatures are limited in their design when they are supposed to be usable for link creation with fromMethodCall. Aside from needing a proper parameter signature, there is a technical limitation on the return type (namely, generating a runtime proxy for link builder invocations), so the return type must not be final. In particular, the common String return type for view names does not work here. You should use ModelAndView or even plain Object (with a String return value) instead.

The earlier examples use static methods in MvcUriComponentsBuilder. Internally, they rely on ServletUriComponentsBuilder to prepare a base URL from the scheme, host, port, context path, and servlet path of the current request. This works well in most cases. However, sometimes, it can be insufficient. For example, you may be outside the context of a request (such as a batch process that prepares links) or perhaps you need to insert a path prefix (such as a locale prefix that was removed from the request path and needs to be re-inserted into links).

For such cases, you can use the static fromXxx overloaded methods that accept a UriComponentsBuilder to use a base URL. Alternatively, you can create an instance of MvcUriComponentsBuilder with a base URL and then use the instance-based withXxx methods. For example, the following listing uses withMethodCall:

Java

UriComponentsBuilder base = ServletUriComponentsBuilder.fromCurrentContextPath().path("/en");
MvcUriComponentsBuilder builder = MvcUriComponentsBuilder.relativeTo(base);
builder.withMethodCall(on(BookingController.class).getBooking(21)).buildAndExpand(42);

URI uri = uriComponents.encode().toUri();

Kotlin

val base = ServletUriComponentsBuilder.fromCurrentContextPath().path("/en")
val builder = MvcUriComponentsBuilder.relativeTo(base)
builder.withMethodCall(on(BookingController::class.java).getBooking(21)).buildAndExpand(42)

val uri = uriComponents.encode().toUri()

Note	As of 5.1, MvcUriComponentsBuilder ignores information from the Forwarded and X-Forwarded-* headers, which specify the client-originated address. Consider using the ForwardedHeaderFilter to extract and use or to discard such headers.

Links in Views

In views such as Thymeleaf, FreeMarker, or JSP, you can build links to annotated controllers by referring to the implicitly or explicitly assigned name for each request mapping.

Consider the following example:

Java

@RequestMapping("/people/{id}/addresses")
public class PersonAddressController {

	@RequestMapping("/{country}")
	public HttpEntity<PersonAddress> getAddress(@PathVariable String country) { ... }
}

Kotlin

@RequestMapping("/people/{id}/addresses")
class PersonAddressController {

	@RequestMapping("/{country}")
	fun getAddress(@PathVariable country: String): HttpEntity<PersonAddress> { ... }
}

Given the preceding controller, you can prepare a link from a JSP, as follows:

<%@ taglib uri="http://www.springframework.org/tags" prefix="s" %>
...
<a href="${s:mvcUrl('PAC#getAddress').arg(0,'US').buildAndExpand('123')}">Get Address</a>

The preceding example relies on the mvcUrl function declared in the Spring tag library (that is, META-INF/spring.tld), but it is easy to define your own function or prepare a similar one for other templating technologies.

Here is how this works. On startup, every @RequestMapping is assigned a default name through HandlerMethodMappingNamingStrategy, whose default implementation uses the capital letters of the class and the method name (for example, the getThing method in ThingController becomes "TC#getThing"). If there is a name clash, you can use @RequestMapping(name="..") to assign an explicit name or implement your own HandlerMethodMappingNamingStrategy.

Asynchronous Requests

Compared to WebFlux

Spring MVC has an extensive integration with Servlet 3.0 asynchronous request processing:

• DeferredResult and Callable return values in controller methods provide basic support for a single asynchronous return value.

• Controllers can stream multiple values, including SSE and raw data.

• Controllers can use reactive clients and return reactive types for response handling.

DeferredResult

Compared to WebFlux

Once the asynchronous request processing feature is enabled in the Servlet container, controller methods can wrap any supported controller method return value with DeferredResult, as the following example shows:

Java

@GetMapping("/quotes")
@ResponseBody
public DeferredResult<String> quotes() {
	DeferredResult<String> deferredResult = new DeferredResult<String>();
	// Save the deferredResult somewhere..
	return deferredResult;
}

// From some other thread...
deferredResult.setResult(result);

Kotlin

@GetMapping("/quotes")
@ResponseBody
fun quotes(): DeferredResult<String> {
	val deferredResult = DeferredResult<String>()
	// Save the deferredResult somewhere..
	return deferredResult
}

// From some other thread...
deferredResult.setResult(result)

The controller can produce the return value asynchronously, from a different thread — for example, in response to an external event (JMS message), a scheduled task, or other event.

Callable

Compared to WebFlux

A controller can wrap any supported return value with java.util.concurrent.Callable, as the following example shows:

Java

@PostMapping
public Callable<String> processUpload(final MultipartFile file) {

	return new Callable<String>() {
		public String call() throws Exception {
			// ...
			return "someView";
		}
	};
}

Kotlin

@PostMapping
fun processUpload(file: MultipartFile) = Callable<String> {
	// ...
	"someView"
}

The return value can then be obtained by running the given task through the configured TaskExecutor.

Processing

Compared to WebFlux

Here is a very concise overview of Servlet asynchronous request processing:

• A ServletRequest can be put in asynchronous mode by calling request.startAsync(). The main effect of doing so is that the Servlet (as well as any filters) can exit, but the response remains open to let processing complete later.

• The call to request.startAsync() returns AsyncContext, which you can use for further control over asynchronous processing. For example, it provides the dispatch method, which is similar to a forward from the Servlet API, except that it lets an application resume request processing on a Servlet container thread.

• The ServletRequest provides access to the current DispatcherType, which you can use to distinguish between processing the initial request, an asynchronous dispatch, a forward, and other dispatcher types.

DeferredResult processing works as follows:

• The controller returns a DeferredResult and saves it in some in-memory queue or list where it can be accessed.

• Spring MVC calls request.startAsync().

• Meanwhile, the DispatcherServlet and all configured filters exit the request processing thread, but the response remains open.

• The application sets the DeferredResult from some thread, and Spring MVC dispatches the request back to the Servlet container.

• The DispatcherServlet is invoked again, and processing resumes with the asynchronously produced return value.

Callable processing works as follows:

• The controller returns a Callable.

• Spring MVC calls request.startAsync() and submits the Callable to a TaskExecutor for processing in a separate thread.

• Meanwhile, the DispatcherServlet and all filters exit the Servlet container thread, but the response remains open.

• Eventually the Callable produces a result, and Spring MVC dispatches the request back to the Servlet container to complete processing.

• The DispatcherServlet is invoked again, and processing resumes with the asynchronously produced return value from the Callable.

For further background and context, you can also read the blog posts that introduced asynchronous request processing support in Spring MVC 3.2.

Exception Handling

When you use a DeferredResult, you can choose whether to call setResult or setErrorResult with an exception. In both cases, Spring MVC dispatches the request back to the Servlet container to complete processing. It is then treated either as if the controller method returned the given value or as if it produced the given exception. The exception then goes through the regular exception handling mechanism (for example, invoking @ExceptionHandler methods).

When you use Callable, similar processing logic occurs, the main difference being that the result is returned from the Callable or an exception is raised by it.

Interception

HandlerInterceptor instances can be of type AsyncHandlerInterceptor, to receive the afterConcurrentHandlingStarted callback on the initial request that starts asynchronous processing (instead of postHandle and afterCompletion).

HandlerInterceptor implementations can also register a CallableProcessingInterceptor or a DeferredResultProcessingInterceptor, to integrate more deeply with the lifecycle of an asynchronous request (for example, to handle a timeout event). See {api-spring-framework}/web/servlet/AsyncHandlerInterceptor.html[AsyncHandlerInterceptor] for more details.

DeferredResult provides onTimeout(Runnable) and onCompletion(Runnable) callbacks. See the {api-spring-framework}/web/context/request/async/DeferredResult.html[javadoc of DeferredResult] for more details. Callable can be substituted for WebAsyncTask that exposes additional methods for timeout and completion callbacks.

Compared to WebFlux

The Servlet API was originally built for making a single pass through the Filter-Servlet chain. Asynchronous request processing, added in Servlet 3.0, lets applications exit the Filter-Servlet chain but leave the response open for further processing. The Spring MVC asynchronous support is built around that mechanism. When a controller returns a DeferredResult, the Filter-Servlet chain is exited, and the Servlet container thread is released. Later, when the DeferredResult is set, an ASYNC dispatch (to the same URL) is made, during which the controller is mapped again but, rather than invoking it, the DeferredResult value is used (as if the controller returned it) to resume processing.

By contrast, Spring WebFlux is neither built on the Servlet API, nor does it need such an asynchronous request processing feature, because it is asynchronous by design. Asynchronous handling is built into all framework contracts and is intrinsically supported through all stages of request processing.

From a programming model perspective, both Spring MVC and Spring WebFlux support asynchronous and Reactive Types as return values in controller methods. Spring MVC even supports streaming, including reactive back pressure. However, individual writes to the response remain blocking (and are performed on a separate thread), unlike WebFlux, which relies on non-blocking I/O and does not need an extra thread for each write.

Another fundamental difference is that Spring MVC does not support asynchronous or reactive types in controller method arguments (for example, @RequestBody, @RequestPart, and others), nor does it have any explicit support for asynchronous and reactive types as model attributes. Spring WebFlux does support all that.

HTTP Streaming

WebFlux

You can use DeferredResult and Callable for a single asynchronous return value. What if you want to produce multiple asynchronous values and have those written to the response? This section describes how to do so.

Objects

You can use the ResponseBodyEmitter return value to produce a stream of objects, where each object is serialized with an HttpMessageConverter and written to the response, as the following example shows:

Java

@GetMapping("/events")
public ResponseBodyEmitter handle() {
	ResponseBodyEmitter emitter = new ResponseBodyEmitter();
	// Save the emitter somewhere..
	return emitter;
}

// In some other thread
emitter.send("Hello once");

// and again later on
emitter.send("Hello again");

// and done at some point
emitter.complete();

Kotlin

@GetMapping("/events")
fun handle() = ResponseBodyEmitter().apply {
	// Save the emitter somewhere..
}

// In some other thread
emitter.send("Hello once")

// and again later on
emitter.send("Hello again")

// and done at some point
emitter.complete()

You can also use ResponseBodyEmitter as the body in a ResponseEntity, letting you customize the status and headers of the response.

When an emitter throws an IOException (for example, if the remote client went away), applications are not responsible for cleaning up the connection and should not invoke emitter.complete or emitter.completeWithError. Instead, the servlet container automatically initiates an AsyncListener error notification, in which Spring MVC makes a completeWithError call. This call, in turn, performs one final ASYNC dispatch to the application, during which Spring MVC invokes the configured exception resolvers and completes the request.

SSE

SseEmitter (a subclass of ResponseBodyEmitter) provides support for Server-Sent Events, where events sent from the server are formatted according to the W3C SSE specification. To produce an SSE stream from a controller, return SseEmitter, as the following example shows:

Java

@GetMapping(path="/events", produces=MediaType.TEXT_EVENT_STREAM_VALUE)
public SseEmitter handle() {
	SseEmitter emitter = new SseEmitter();
	// Save the emitter somewhere..
	return emitter;
}

// In some other thread
emitter.send("Hello once");

// and again later on
emitter.send("Hello again");

// and done at some point
emitter.complete();

Kotlin

@GetMapping("/events", produces = [MediaType.TEXT_EVENT_STREAM_VALUE])
fun handle() = SseEmitter().apply {
	// Save the emitter somewhere..
}

// In some other thread
emitter.send("Hello once")

// and again later on
emitter.send("Hello again")

// and done at some point
emitter.complete()

While SSE is the main option for streaming into browsers, note that Internet Explorer does not support Server-Sent Events. Consider using Spring’s WebSocket messaging with SockJS fallback transports (including SSE) that target a wide range of browsers.

See also previous section for notes on exception handling.

Raw Data

Sometimes, it is useful to bypass message conversion and stream directly to the response OutputStream (for example, for a file download). You can use the StreamingResponseBody return value type to do so, as the following example shows:

Java

@GetMapping("/download")
public StreamingResponseBody handle() {
	return new StreamingResponseBody() {
		@Override
		public void writeTo(OutputStream outputStream) throws IOException {
			// write...
		}
	};
}

Kotlin

@GetMapping("/download")
fun handle() = StreamingResponseBody {
	// write...
}

You can use StreamingResponseBody as the body in a ResponseEntity to customize the status and headers of the response.

Reactive Types

WebFlux

Spring MVC supports use of reactive client libraries in a controller (also read Reactive Libraries in the WebFlux section). This includes the WebClient from spring-webflux and others, such as Spring Data reactive data repositories. In such scenarios, it is convenient to be able to return reactive types from the controller method.

Reactive return values are handled as follows:

• A single-value promise is adapted to, similar to using DeferredResult. Examples include Mono (Reactor) or Single (RxJava).

• A multi-value stream with a streaming media type (such as application/x-ndjson or text/event-stream) is adapted to, similar to using ResponseBodyEmitter or SseEmitter. Examples include Flux (Reactor) or Observable (RxJava). Applications can also return Flux<ServerSentEvent> or Observable<ServerSentEvent>.

• A multi-value stream with any other media type (such as application/json) is adapted to, similar to using DeferredResult<List<?>>.

Tip	Spring MVC supports Reactor and RxJava through the {api-spring-framework}/core/ReactiveAdapterRegistry.html[ReactiveAdapterRegistry] from spring-core, which lets it adapt from multiple reactive libraries.

For streaming to the response, reactive back pressure is supported, but writes to the response are still blocking and are run on a separate thread through the configured TaskExecutor, to avoid blocking the upstream source (such as a Flux returned from WebClient). By default, SimpleAsyncTaskExecutor is used for the blocking writes, but that is not suitable under load. If you plan to stream with a reactive type, you should use the MVC configuration to configure a task executor.

Disconnects

WebFlux

The Servlet API does not provide any notification when a remote client goes away. Therefore, while streaming to the response, whether through SseEmitter or reactive types, it is important to send data periodically, since the write fails if the client has disconnected. The send could take the form of an empty (comment-only) SSE event or any other data that the other side would have to interpret as a heartbeat and ignore.

Alternatively, consider using web messaging solutions (such as STOMP over WebSocket or WebSocket with SockJS) that have a built-in heartbeat mechanism.

Configuration

Compared to WebFlux

The asynchronous request processing feature must be enabled at the Servlet container level. The MVC configuration also exposes several options for asynchronous requests.

Servlet Container

Filter and Servlet declarations have an asyncSupported flag that needs to be set to true to enable asynchronous request processing. In addition, Filter mappings should be declared to handle the ASYNC javax.servlet.DispatchType.

In Java configuration, when you use AbstractAnnotationConfigDispatcherServletInitializer to initialize the Servlet container, this is done automatically.

In web.xml configuration, you can add <async-supported>true</async-supported> to the DispatcherServlet and to Filter declarations and add <dispatcher>ASYNC</dispatcher> to filter mappings.

Spring MVC

The MVC configuration exposes the following options related to asynchronous request processing:

• Java configuration: Use the configureAsyncSupport callback on WebMvcConfigurer.

• XML namespace: Use the <async-support> element under <mvc:annotation-driven>.

You can configure the following:

• Default timeout value for async requests, which if not set, depends on the underlying Servlet container.

• AsyncTaskExecutor to use for blocking writes when streaming with Reactive Types and for executing Callable instances returned from controller methods. We highly recommended configuring this property if you stream with reactive types or have controller methods that return Callable, since by default, it is a SimpleAsyncTaskExecutor.

• DeferredResultProcessingInterceptor implementations and CallableProcessingInterceptor implementations.

Note that you can also set the default timeout value on a DeferredResult, a ResponseBodyEmitter, and an SseEmitter. For a Callable, you can use WebAsyncTask to provide a timeout value.

webmvc-cors.adoc

Web Security

WebFlux

The Spring Security project provides support for protecting web applications from malicious exploits. See the Spring Security reference documentation, including:

• {doc-root}/spring-security/reference/servlet/integrations/mvc.html[Spring MVC Security]

• {doc-root}/spring-security/reference/servlet/test/mockmvc/setup.html[Spring MVC Test Support]

• {doc-root}/spring-security/reference/features/exploits/csrf.html#csrf-protection[CSRF protection]

• {doc-root}/spring-security/reference/features/exploits/headers.html[Security Response Headers]

HDIV is another web security framework that integrates with Spring MVC.

HTTP Caching

WebFlux

HTTP caching can significantly improve the performance of a web application. HTTP caching revolves around the Cache-Control response header and, subsequently, conditional request headers (such as Last-Modified and ETag). Cache-Control advises private (for example, browser) and public (for example, proxy) caches on how to cache and re-use responses. An ETag header is used to make a conditional request that may result in a 304 (NOT_MODIFIED) without a body, if the content has not changed. ETag can be seen as a more sophisticated successor to the Last-Modified header.

This section describes the HTTP caching-related options that are available in Spring Web MVC.

CacheControl

WebFlux

{api-spring-framework}/http/CacheControl.html[CacheControl] provides support for configuring settings related to the Cache-Control header and is accepted as an argument in a number of places:

• {api-spring-framework}/web/servlet/mvc/WebContentInterceptor.html[WebContentInterceptor]

• {api-spring-framework}/web/servlet/support/WebContentGenerator.html[WebContentGenerator]

• Controllers

• Static Resources

While RFC 7234 describes all possible directives for the Cache-Control response header, the CacheControl type takes a use case-oriented approach that focuses on the common scenarios:

Java

// Cache for an hour - "Cache-Control: max-age=3600"
CacheControl ccCacheOneHour = CacheControl.maxAge(1, TimeUnit.HOURS);

// Prevent caching - "Cache-Control: no-store"
CacheControl ccNoStore = CacheControl.noStore();

// Cache for ten days in public and private caches,
// public caches should not transform the response
// "Cache-Control: max-age=864000, public, no-transform"
CacheControl ccCustom = CacheControl.maxAge(10, TimeUnit.DAYS).noTransform().cachePublic();

Kotlin

// Cache for an hour - "Cache-Control: max-age=3600"
val ccCacheOneHour = CacheControl.maxAge(1, TimeUnit.HOURS)

// Prevent caching - "Cache-Control: no-store"
val ccNoStore = CacheControl.noStore()

// Cache for ten days in public and private caches,
// public caches should not transform the response
// "Cache-Control: max-age=864000, public, no-transform"
val ccCustom = CacheControl.maxAge(10, TimeUnit.DAYS).noTransform().cachePublic()

WebContentGenerator also accepts a simpler cachePeriod property (defined in seconds) that works as follows:

• A -1 value does not generate a Cache-Control response header.

• A 0 value prevents caching by using the 'Cache-Control: no-store' directive.

• An n > 0 value caches the given response for n seconds by using the 'Cache-Control: max-age=n' directive.

Controllers

WebFlux

Controllers can add explicit support for HTTP caching. We recommended doing so, since the lastModified or ETag value for a resource needs to be calculated before it can be compared against conditional request headers. A controller can add an ETag header and Cache-Control settings to a ResponseEntity, as the following example shows:

Java

@GetMapping("/book/{id}")
public ResponseEntity<Book> showBook(@PathVariable Long id) {

	Book book = findBook(id);
	String version = book.getVersion();

	return ResponseEntity
			.ok()
			.cacheControl(CacheControl.maxAge(30, TimeUnit.DAYS))
			.eTag(version) // lastModified is also available
			.body(book);
}

Kotlin

@GetMapping("/book/{id}")
fun showBook(@PathVariable id: Long): ResponseEntity<Book> {

	val book = findBook(id);
	val version = book.getVersion()

	return ResponseEntity
			.ok()
			.cacheControl(CacheControl.maxAge(30, TimeUnit.DAYS))
			.eTag(version) // lastModified is also available
			.body(book)
}

The preceding example sends a 304 (NOT_MODIFIED) response with an empty body if the comparison to the conditional request headers indicates that the content has not changed. Otherwise, the ETag and Cache-Control headers are added to the response.

You can also make the check against conditional request headers in the controller, as the following example shows:

Java

@RequestMapping
public String myHandleMethod(WebRequest request, Model model) {

	long eTag = ... // (1)

	if (request.checkNotModified(eTag)) {
		return null; // (2)
	}

	model.addAttribute(...); // (3)
	return "myViewName";
}

1. Application-specific calculation.

2. The response has been set to 304 (NOT_MODIFIED) — no further processing.

3. Continue with the request processing.

Kotlin

@RequestMapping
fun myHandleMethod(request: WebRequest, model: Model): String? {

	val eTag: Long = ... // (1)

	if (request.checkNotModified(eTag)) {
		return null // (2)
	}

	model[...] = ... // (3)
	return "myViewName"
}

1. Application-specific calculation.

2. The response has been set to 304 (NOT_MODIFIED) — no further processing.

3. Continue with the request processing.

There are three variants for checking conditional requests against eTag values, lastModified values, or both. For conditional GET and HEAD requests, you can set the response to 304 (NOT_MODIFIED). For conditional POST, PUT, and DELETE, you can instead set the response to 412 (PRECONDITION_FAILED), to prevent concurrent modification.

Static Resources

WebFlux

You should serve static resources with a Cache-Control and conditional response headers for optimal performance. See the section on configuring Static Resources.

ETag Filter

You can use the ShallowEtagHeaderFilter to add “shallow” eTag values that are computed from the response content and, thus, save bandwidth but not CPU time. See Shallow ETag.

webmvc-view.adoc

MVC Config

WebFlux

The MVC Java configuration and the MVC XML namespace provide default configuration suitable for most applications and a configuration API to customize it.

For more advanced customizations, which are not available in the configuration API, see Advanced Java Config and Advanced XML Config.

You do not need to understand the underlying beans created by the MVC Java configuration and the MVC namespace. If you want to learn more, see Special Bean Types and Web MVC Config.

Enable MVC Configuration

WebFlux

In Java configuration, you can use the @EnableWebMvc annotation to enable MVC configuration, as the following example shows:

Java

@Configuration
@EnableWebMvc
public class WebConfig {
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig

In XML configuration, you can use the <mvc:annotation-driven> element to enable MVC configuration, as the following example shows:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:mvc="http://www.springframework.org/schema/mvc"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="
		http://www.springframework.org/schema/beans
		https://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/mvc
		https://www.springframework.org/schema/mvc/spring-mvc.xsd">

	<mvc:annotation-driven/>

</beans>

The preceding example registers a number of Spring MVC infrastructure beans and adapts to dependencies available on the classpath (for example, payload converters for JSON, XML, and others).

MVC Config API

WebFlux

In Java configuration, you can implement the WebMvcConfigurer interface, as the following example shows:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	// Implement configuration methods...
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	// Implement configuration methods...
}

In XML, you can check attributes and sub-elements of <mvc:annotation-driven/>. You can view the Spring MVC XML schema or use the code completion feature of your IDE to discover what attributes and sub-elements are available.

Type Conversion

WebFlux

By default, formatters for various number and date types are installed, along with support for customization via @NumberFormat and @DateTimeFormat on fields.

To register custom formatters and converters in Java config, use the following:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public void addFormatters(FormatterRegistry registry) {
		// ...
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun addFormatters(registry: FormatterRegistry) {
		// ...
	}
}

To do the same in XML config, use the following:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:mvc="http://www.springframework.org/schema/mvc"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="
		http://www.springframework.org/schema/beans
		https://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/mvc
		https://www.springframework.org/schema/mvc/spring-mvc.xsd">

	<mvc:annotation-driven conversion-service="conversionService"/>

	<bean id="conversionService"
			class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
		<property name="converters">
			<set>
				<bean class="org.example.MyConverter"/>
			</set>
		</property>
		<property name="formatters">
			<set>
				<bean class="org.example.MyFormatter"/>
				<bean class="org.example.MyAnnotationFormatterFactory"/>
			</set>
		</property>
		<property name="formatterRegistrars">
			<set>
				<bean class="org.example.MyFormatterRegistrar"/>
			</set>
		</property>
	</bean>

</beans>

By default Spring MVC considers the request Locale when parsing and formatting date values. This works for forms where dates are represented as Strings with "input" form fields. For "date" and "time" form fields, however, browsers use a fixed format defined in the HTML spec. For such cases date and time formatting can be customized as follows:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public void addFormatters(FormatterRegistry registry) {
		DateTimeFormatterRegistrar registrar = new DateTimeFormatterRegistrar();
		registrar.setUseIsoFormat(true);
		registrar.registerFormatters(registry);
     	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun addFormatters(registry: FormatterRegistry) {
		val registrar = DateTimeFormatterRegistrar()
		registrar.setUseIsoFormat(true)
		registrar.registerFormatters(registry)
	}
}

Note	See the FormatterRegistrar SPI and the FormattingConversionServiceFactoryBean for more information on when to use FormatterRegistrar implementations.

Validation

WebFlux

By default, if Bean Validation is present on the classpath (for example, Hibernate Validator), the LocalValidatorFactoryBean is registered as a global Validator for use with @Valid and Validated on controller method arguments.

In Java configuration, you can customize the global Validator instance, as the following example shows:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public Validator getValidator() {
		// ...
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun getValidator(): Validator {
		// ...
	}
}

The following example shows how to achieve the same configuration in XML:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:mvc="http://www.springframework.org/schema/mvc"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="
		http://www.springframework.org/schema/beans
		https://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/mvc
		https://www.springframework.org/schema/mvc/spring-mvc.xsd">

	<mvc:annotation-driven validator="globalValidator"/>

</beans>

Note that you can also register Validator implementations locally, as the following example shows:

Java

@Controller
public class MyController {

	@InitBinder
	protected void initBinder(WebDataBinder binder) {
		binder.addValidators(new FooValidator());
	}
}

Kotlin

@Controller
class MyController {

	@InitBinder
	protected fun initBinder(binder: WebDataBinder) {
		binder.addValidators(FooValidator())
	}
}

Tip	If you need to have a LocalValidatorFactoryBean injected somewhere, create a bean and mark it with @Primary in order to avoid conflict with the one declared in the MVC configuration.

Interceptors

In Java configuration, you can register interceptors to apply to incoming requests, as the following example shows:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public void addInterceptors(InterceptorRegistry registry) {
		registry.addInterceptor(new LocaleChangeInterceptor());
		registry.addInterceptor(new ThemeChangeInterceptor()).addPathPatterns("/**").excludePathPatterns("/admin/**");
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun addInterceptors(registry: InterceptorRegistry) {
		registry.addInterceptor(LocaleChangeInterceptor())
		registry.addInterceptor(ThemeChangeInterceptor()).addPathPatterns("/**").excludePathPatterns("/admin/**")
	}
}

The following example shows how to achieve the same configuration in XML:

<mvc:interceptors>
	<bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"/>
	<mvc:interceptor>
		<mvc:mapping path="/**"/>
		<mvc:exclude-mapping path="/admin/**"/>
		<bean class="org.springframework.web.servlet.theme.ThemeChangeInterceptor"/>
	</mvc:interceptor>
</mvc:interceptors>

Note

Mapped interceptors are not ideally suited as a security layer due to the potential for a mismatch with annotated controller path matching, which can also match trailing slashes and path extensions transparently, along with other path matching options. Many of these options have been deprecated but the potential for a mismatch remains. Generally, we recommend using Spring Security which includes a dedicated MvcRequestMatcher to align with Spring MVC path matching and also has a security firewall that blocks many unwanted characters in URL paths.

Content Types

WebFlux

You can configure how Spring MVC determines the requested media types from the request (for example, Accept header, URL path extension, query parameter, and others).

By default, only the Accept header is checked.

If you must use URL-based content type resolution, consider using the query parameter strategy over path extensions. See Suffix Match and Suffix Match and RFD for more details.

In Java configuration, you can customize requested content type resolution, as the following example shows:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
		configurer.mediaType("json", MediaType.APPLICATION_JSON);
		configurer.mediaType("xml", MediaType.APPLICATION_XML);
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun configureContentNegotiation(configurer: ContentNegotiationConfigurer) {
		configurer.mediaType("json", MediaType.APPLICATION_JSON)
		configurer.mediaType("xml", MediaType.APPLICATION_XML)
	}
}

The following example shows how to achieve the same configuration in XML:

<mvc:annotation-driven content-negotiation-manager="contentNegotiationManager"/>

<bean id="contentNegotiationManager" class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
	<property name="mediaTypes">
		<value>
			json=application/json
			xml=application/xml
		</value>
	</property>
</bean>

Message Converters

WebFlux

You can customize HttpMessageConverter in Java configuration by overriding {api-spring-framework}/web/servlet/config/annotation/WebMvcConfigurer.html#configureMessageConverters-java.util.List-[configureMessageConverters()] (to replace the default converters created by Spring MVC) or by overriding {api-spring-framework}/web/servlet/config/annotation/WebMvcConfigurer.html#extendMessageConverters-java.util.List-[extendMessageConverters()] (to customize the default converters or add additional converters to the default ones).

The following example adds XML and Jackson JSON converters with a customized ObjectMapper instead of the default ones:

Java

@Configuration
@EnableWebMvc
public class WebConfiguration implements WebMvcConfigurer {

	@Override
	public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
		Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder()
				.indentOutput(true)
				.dateFormat(new SimpleDateFormat("yyyy-MM-dd"))
				.modulesToInstall(new ParameterNamesModule());
		converters.add(new MappingJackson2HttpMessageConverter(builder.build()));
		converters.add(new MappingJackson2XmlHttpMessageConverter(builder.createXmlMapper(true).build()));
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfiguration : WebMvcConfigurer {

	override fun configureMessageConverters(converters: MutableList<HttpMessageConverter<*>>) {
		val builder = Jackson2ObjectMapperBuilder()
				.indentOutput(true)
				.dateFormat(SimpleDateFormat("yyyy-MM-dd"))
				.modulesToInstall(ParameterNamesModule())
		converters.add(MappingJackson2HttpMessageConverter(builder.build()))
		converters.add(MappingJackson2XmlHttpMessageConverter(builder.createXmlMapper(true).build()))

In the preceding example, {api-spring-framework}/http/converter/json/Jackson2ObjectMapperBuilder.html[Jackson2ObjectMapperBuilder] is used to create a common configuration for both MappingJackson2HttpMessageConverter and MappingJackson2XmlHttpMessageConverter with indentation enabled, a customized date format, and the registration of jackson-module-parameter-names, Which adds support for accessing parameter names (a feature added in Java 8).

This builder customizes Jackson’s default properties as follows:

• DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES is disabled.

• MapperFeature.DEFAULT_VIEW_INCLUSION is disabled.

It also automatically registers the following well-known modules if they are detected on the classpath:

• jackson-datatype-joda: Support for Joda-Time types.

• jackson-datatype-jsr310: Support for Java 8 Date and Time API types.

• jackson-datatype-jdk8: Support for other Java 8 types, such as Optional.

• jackson-module-kotlin: Support for Kotlin classes and data classes.

Note	Enabling indentation with Jackson XML support requires woodstox-core-asl dependency in addition to jackson-dataformat-xml one.

Other interesting Jackson modules are available:

• jackson-datatype-money: Support for javax.money types (unofficial module).

• jackson-datatype-hibernate: Support for Hibernate-specific types and properties (including lazy-loading aspects).

The following example shows how to achieve the same configuration in XML:

<mvc:annotation-driven>
	<mvc:message-converters>
		<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
			<property name="objectMapper" ref="objectMapper"/>
		</bean>
		<bean class="org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter">
			<property name="objectMapper" ref="xmlMapper"/>
		</bean>
	</mvc:message-converters>
</mvc:annotation-driven>

<bean id="objectMapper" class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean"
	  p:indentOutput="true"
	  p:simpleDateFormat="yyyy-MM-dd"
	  p:modulesToInstall="com.fasterxml.jackson.module.paramnames.ParameterNamesModule"/>

<bean id="xmlMapper" parent="objectMapper" p:createXmlMapper="true"/>

View Controllers

This is a shortcut for defining a ParameterizableViewController that immediately forwards to a view when invoked. You can use it in static cases when there is no Java controller logic to run before the view generates the response.

The following example of Java configuration forwards a request for / to a view called home:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public void addViewControllers(ViewControllerRegistry registry) {
		registry.addViewController("/").setViewName("home");
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun addViewControllers(registry: ViewControllerRegistry) {
		registry.addViewController("/").setViewName("home")
	}
}

The following example achieves the same thing as the preceding example, but with XML, by using the <mvc:view-controller> element:

<mvc:view-controller path="/" view-name="home"/>

If an @RequestMapping method is mapped to a URL for any HTTP method then a view controller cannot be used to handle the same URL. This is because a match by URL to an annotated controller is considered a strong enough indication of endpoint ownership so that a 405 (METHOD_NOT_ALLOWED), a 415 (UNSUPPORTED_MEDIA_TYPE), or similar response can be sent to the client to help with debugging. For this reason it is recommended to avoid splitting URL handling across an annotated controller and a view controller.

View Resolvers

WebFlux

The MVC configuration simplifies the registration of view resolvers.

The following Java configuration example configures content negotiation view resolution by using JSP and Jackson as a default View for JSON rendering:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public void configureViewResolvers(ViewResolverRegistry registry) {
		registry.enableContentNegotiation(new MappingJackson2JsonView());
		registry.jsp();
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun configureViewResolvers(registry: ViewResolverRegistry) {
		registry.enableContentNegotiation(MappingJackson2JsonView())
		registry.jsp()
	}
}

The following example shows how to achieve the same configuration in XML:

<mvc:view-resolvers>
	<mvc:content-negotiation>
		<mvc:default-views>
			<bean class="org.springframework.web.servlet.view.json.MappingJackson2JsonView"/>
		</mvc:default-views>
	</mvc:content-negotiation>
	<mvc:jsp/>
</mvc:view-resolvers>

Note, however, that FreeMarker, Tiles, Groovy Markup, and script templates also require configuration of the underlying view technology.

The MVC namespace provides dedicated elements. The following example works with FreeMarker:

<mvc:view-resolvers>
	<mvc:content-negotiation>
		<mvc:default-views>
			<bean class="org.springframework.web.servlet.view.json.MappingJackson2JsonView"/>
		</mvc:default-views>
	</mvc:content-negotiation>
	<mvc:freemarker cache="false"/>
</mvc:view-resolvers>

<mvc:freemarker-configurer>
	<mvc:template-loader-path location="/freemarker"/>
</mvc:freemarker-configurer>

In Java configuration, you can add the respective Configurer bean, as the following example shows:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public void configureViewResolvers(ViewResolverRegistry registry) {
		registry.enableContentNegotiation(new MappingJackson2JsonView());
		registry.freeMarker().cache(false);
	}

	@Bean
	public FreeMarkerConfigurer freeMarkerConfigurer() {
		FreeMarkerConfigurer configurer = new FreeMarkerConfigurer();
		configurer.setTemplateLoaderPath("/freemarker");
		return configurer;
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun configureViewResolvers(registry: ViewResolverRegistry) {
		registry.enableContentNegotiation(MappingJackson2JsonView())
		registry.freeMarker().cache(false)
	}

	@Bean
	fun freeMarkerConfigurer() = FreeMarkerConfigurer().apply {
		setTemplateLoaderPath("/freemarker")
	}
}

Static Resources

WebFlux

This option provides a convenient way to serve static resources from a list of {api-spring-framework}/core/io/Resource.html[Resource]-based locations.

In the next example, given a request that starts with /resources, the relative path is used to find and serve static resources relative to /public under the web application root or on the classpath under /static. The resources are served with a one-year future expiration to ensure maximum use of the browser cache and a reduction in HTTP requests made by the browser. The Last-Modified information is deduced from Resource#lastModified so that HTTP conditional requests are supported with "Last-Modified" headers.

The following listing shows how to do so with Java configuration:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public void addResourceHandlers(ResourceHandlerRegistry registry) {
		registry.addResourceHandler("/resources/**")
				.addResourceLocations("/public", "classpath:/static/")
				.setCacheControl(CacheControl.maxAge(Duration.ofDays(365)));
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun addResourceHandlers(registry: ResourceHandlerRegistry) {
		registry.addResourceHandler("/resources/**")
				.addResourceLocations("/public", "classpath:/static/")
				.setCacheControl(CacheControl.maxAge(Duration.ofDays(365)))
	}
}

The following example shows how to achieve the same configuration in XML:

<mvc:resources mapping="/resources/**"
	location="/public, classpath:/static/"
	cache-period="31556926" />

See also HTTP caching support for static resources.

The resource handler also supports a chain of {api-spring-framework}/web/servlet/resource/ResourceResolver.html[ResourceResolver] implementations and {api-spring-framework}/web/servlet/resource/ResourceTransformer.html[ResourceTransformer] implementations, which you can use to create a toolchain for working with optimized resources.

You can use the VersionResourceResolver for versioned resource URLs based on an MD5 hash computed from the content, a fixed application version, or other. A ContentVersionStrategy (MD5 hash) is a good choice — with some notable exceptions, such as JavaScript resources used with a module loader.

The following example shows how to use VersionResourceResolver in Java configuration:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public void addResourceHandlers(ResourceHandlerRegistry registry) {
		registry.addResourceHandler("/resources/**")
				.addResourceLocations("/public/")
				.resourceChain(true)
				.addResolver(new VersionResourceResolver().addContentVersionStrategy("/**"));
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun addResourceHandlers(registry: ResourceHandlerRegistry) {
		registry.addResourceHandler("/resources/**")
				.addResourceLocations("/public/")
				.resourceChain(true)
				.addResolver(VersionResourceResolver().addContentVersionStrategy("/**"))
	}
}

The following example shows how to achieve the same configuration in XML:

<mvc:resources mapping="/resources/**" location="/public/">
	<mvc:resource-chain resource-cache="true">
		<mvc:resolvers>
			<mvc:version-resolver>
				<mvc:content-version-strategy patterns="/**"/>
			</mvc:version-resolver>
		</mvc:resolvers>
	</mvc:resource-chain>
</mvc:resources>

You can then use ResourceUrlProvider to rewrite URLs and apply the full chain of resolvers and transformers — for example, to insert versions. The MVC configuration provides a ResourceUrlProvider bean so that it can be injected into others. You can also make the rewrite transparent with the ResourceUrlEncodingFilter for Thymeleaf, JSPs, FreeMarker, and others with URL tags that rely on HttpServletResponse#encodeURL.

Note that, when using both EncodedResourceResolver (for example, for serving gzipped or brotli-encoded resources) and VersionResourceResolver, you must register them in this order. That ensures content-based versions are always computed reliably, based on the unencoded file.

For WebJars, versioned URLs like /webjars/jquery/1.2.0/jquery.min.js are the recommended and most efficient way to use them. The related resource location is configured out of the box with Spring Boot (or can be configured manually via ResourceHandlerRegistry) and does not require to add the org.webjars:webjars-locator-core dependency.

Version-less URLs like /webjars/jquery/jquery.min.js are supported through the WebJarsResourceResolver which is automatically registered when the org.webjars:webjars-locator-core library is present on the classpath, at the cost of a classpath scanning that could slow down application startup. The resolver can re-write URLs to include the version of the jar and can also match against incoming URLs without versions — for example, from /webjars/jquery/jquery.min.js to /webjars/jquery/1.2.0/jquery.min.js.

Tip	The Java configuration based on ResourceHandlerRegistry provides further options for fine-grained control, e.g. last-modified behavior and optimized resource resolution.

Default Servlet

Spring MVC allows for mapping the DispatcherServlet to / (thus overriding the mapping of the container’s default Servlet), while still allowing static resource requests to be handled by the container’s default Servlet. It configures a DefaultServletHttpRequestHandler with a URL mapping of /** and the lowest priority relative to other URL mappings.

This handler forwards all requests to the default Servlet. Therefore, it must remain last in the order of all other URL HandlerMappings. That is the case if you use <mvc:annotation-driven>. Alternatively, if you set up your own customized HandlerMapping instance, be sure to set its order property to a value lower than that of the DefaultServletHttpRequestHandler, which is Integer.MAX_VALUE.

The following example shows how to enable the feature by using the default setup:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
		configurer.enable();
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun configureDefaultServletHandling(configurer: DefaultServletHandlerConfigurer) {
		configurer.enable()
	}
}

The following example shows how to achieve the same configuration in XML:

<mvc:default-servlet-handler/>

The caveat to overriding the / Servlet mapping is that the RequestDispatcher for the default Servlet must be retrieved by name rather than by path. The DefaultServletHttpRequestHandler tries to auto-detect the default Servlet for the container at startup time, using a list of known names for most of the major Servlet containers (including Tomcat, Jetty, GlassFish, JBoss, Resin, WebLogic, and WebSphere). If the default Servlet has been custom-configured with a different name, or if a different Servlet container is being used where the default Servlet name is unknown, then you must explicitly provide the default Servlet’s name, as the following example shows:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
		configurer.enable("myCustomDefaultServlet");
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun configureDefaultServletHandling(configurer: DefaultServletHandlerConfigurer) {
		configurer.enable("myCustomDefaultServlet")
	}
}

The following example shows how to achieve the same configuration in XML:

<mvc:default-servlet-handler default-servlet-name="myCustomDefaultServlet"/>

Path Matching

WebFlux

You can customize options related to path matching and treatment of the URL. For details on the individual options, see the {api-spring-framework}/web/servlet/config/annotation/PathMatchConfigurer.html[PathMatchConfigurer] javadoc.

The following example shows how to customize path matching in Java configuration:

Java

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

	@Override
	public void configurePathMatch(PathMatchConfigurer configurer) {
		configurer
			.setPatternParser(new PathPatternParser())
			.addPathPrefix("/api", HandlerTypePredicate.forAnnotation(RestController.class));
	}

	private PathPatternParser patternParser() {
		// ...
	}
}

Kotlin

@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {

	override fun configurePathMatch(configurer: PathMatchConfigurer) {
		configurer
			.setPatternParser(patternParser)
			.addPathPrefix("/api", HandlerTypePredicate.forAnnotation(RestController::class.java))
	}

	fun patternParser(): PathPatternParser {
		//...
	}
}

The following example shows how to achieve the same configuration in XML:

<mvc:annotation-driven>
	<mvc:path-matching
		trailing-slash="false"
		path-helper="pathHelper"
		path-matcher="pathMatcher"/>
</mvc:annotation-driven>

<bean id="pathHelper" class="org.example.app.MyPathHelper"/>
<bean id="pathMatcher" class="org.example.app.MyPathMatcher"/>

Advanced Java Config

WebFlux

@EnableWebMvc imports DelegatingWebMvcConfiguration, which:

• Provides default Spring configuration for Spring MVC applications

• Detects and delegates to WebMvcConfigurer implementations to customize that configuration.

For advanced mode, you can remove @EnableWebMvc and extend directly from DelegatingWebMvcConfiguration instead of implementing WebMvcConfigurer, as the following example shows:

Java

@Configuration
public class WebConfig extends DelegatingWebMvcConfiguration {

	// ...
}

Kotlin

@Configuration
class WebConfig : DelegatingWebMvcConfiguration() {

	// ...
}

You can keep existing methods in WebConfig, but you can now also override bean declarations from the base class, and you can still have any number of other WebMvcConfigurer implementations on the classpath.

Advanced XML Config

The MVC namespace does not have an advanced mode. If you need to customize a property on a bean that you cannot change otherwise, you can use the BeanPostProcessor lifecycle hook of the Spring ApplicationContext, as the following example shows:

Java

@Component
public class MyPostProcessor implements BeanPostProcessor {

	public Object postProcessBeforeInitialization(Object bean, String name) throws BeansException {
		// ...
	}
}

Kotlin

@Component
class MyPostProcessor : BeanPostProcessor {

	override fun postProcessBeforeInitialization(bean: Any, name: String): Any {
		// ...
	}
}

Note that you need to declare MyPostProcessor as a bean, either explicitly in XML or by letting it be detected through a <component-scan/> declaration.

HTTP/2

WebFlux

Servlet 4 containers are required to support HTTP/2, and Spring Framework 5 is compatible with Servlet API 4. From a programming model perspective, there is nothing specific that applications need to do. However, there are considerations related to server configuration. For more details, see the HTTP/2 wiki page.

The Servlet API does expose one construct related to HTTP/2. You can use the javax.servlet.http.PushBuilder to proactively push resources to clients, and it is supported as a method argument to @RequestMapping methods.