CannotGetJdbcConnectionException in Spring Boot if I use a suspend function in @RestController

[MikeMitterer]

My RestController has this function:

    @GetMapping("/wait")
    suspend fun waitForSeconds(@RequestParam(value = "seconds", defaultValue = "1") seconds: Long): String {
        val now = DateTime.now()
        delay(seconds * 1000)
        val then = DateTime.now()
        return "Diff between: ${then.toDateTimeISO()} and ${now.toDateTimeISO()} is: ${Seconds.secondsBetween(now, then).seconds}sec(s)"
    }

My dependencies are:

implementation("org.springframework.boot:spring-boot-starter-webflux")
...
implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:$kotlinCoroutines_version")
implementation("org.jetbrains.kotlinx:kotlinx-coroutines-reactor:$kotlinCoroutines_version")

[Update]
If I call the "wait"-API-Function
If I start the server
I get

java.lang.TypeNotPresentException: Type org.springframework.jdbc.CannotGetJdbcConnectionException not present
	at java.base/sun.reflect.generics.factory.CoreReflectionFactory.makeNamedType(CoreReflectionFactory.java:117)
	at java.base/sun.reflect.generics.visitor.Reifier.visitClassTypeSignature(Reifier.java:125)
	at java.base/sun.reflect.generics.tree.ClassTypeSignature.accept(ClassTypeSignature.java:49)
	at java.base/sun.reflect.generics.visitor.Reifier.reifyTypeArguments(Reifier.java:68)
	at java.base/sun.reflect.generics.visitor.Reifier.visitClassTypeSignature(Reifier.java:138)
	at java.base/sun.reflect.generics.tree.ClassTypeSignature.accept(ClassTypeSignature.java:49)
	at java.base/sun.reflect.generics.repository.ClassRepository.computeSuperclass(ClassRepository.java:104)
	at java.base/sun.reflect.generics.repository.ClassRepository.getSuperclass(ClassRepository.java:86)
	at java.base/java.lang.Class.getGenericSuperclass(Class.java:955)
	at org.springframework.core.ResolvableType.getSuperType(ResolvableType.java:467)
	at org.springframework.core.ResolvableType.as(ResolvableType.java:456)
	at org.springframework.core.ResolvableType.forClass(ResolvableType.java:1041)
	at org.springframework.boot.diagnostics.AbstractFailureAnalyzer.getCauseType(AbstractFailureAnalyzer.java:56)
	at org.springframework.boot.diagnostics.AbstractFailureAnalyzer.analyze(AbstractFailureAnalyzer.java:33)
	at org.springframework.boot.diagnostics.FailureAnalyzers.analyze(FailureAnalyzers.java:111)
	at org.springframework.boot.diagnostics.FailureAnalyzers.reportException(FailureAnalyzers.java:104)
	at org.springframework.boot.SpringApplication.reportFailure(SpringApplication.java:816)
	at org.springframework.boot.SpringApplication.handleRunFailure(SpringApplication.java:801)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:325)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215)
	at at.mikemitterer.catshostel.Application$Companion.main(Application.kt:46)
	at at.mikemitterer.catshostel.Application.main(Application.kt)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:567)
	at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49)
Caused by: java.lang.ClassNotFoundException: org.springframework.jdbc.CannotGetJdbcConnectionException
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:602)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
	at java.base/java.lang.Class.forName0(Native Method)
	at java.base/java.lang.Class.forName(Class.java:416)
	at java.base/sun.reflect.generics.factory.CoreReflectionFactory.makeNamedType(CoreReflectionFactory.java:114)
	... 27 common frames omitted
2020-05-12 16:03:28.814 [restartedMain] ERROR o.s.boot.SpringApplication - Application run failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'requestMappingHandlerMapping' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Invocation of init method failed; nested exception is java.lang.IllegalStateException: Unsupported suspending handler method detected: public java.lang.Object at.mikemitterer.catshostel.routes.BasicController.waitForSeconds(long,kotlin.coroutines.Continuation)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1796)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:595)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517)
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:226)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:895)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:878)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550)
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747)
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215)
	at at.mikemitterer.catshostel.Application$Companion.main(Application.kt:46)
	at at.mikemitterer.catshostel.Application.main(Application.kt)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:567)
	at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49)
Caused by: java.lang.IllegalStateException: Unsupported suspending handler method detected: public java.lang.Object at.mikemitterer.catshostel.routes.BasicController.waitForSeconds(long,kotlin.coroutines.Continuation)
	at org.springframework.web.servlet.handler.AbstractHandlerMethodMapping$MappingRegistry.register(AbstractHandlerMethodMapping.java:597)
	at org.springframework.web.servlet.handler.AbstractHandlerMethodMapping.registerHandlerMethod(AbstractHandlerMethodMapping.java:318)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping.registerHandlerMethod(RequestMappingHandlerMapping.java:377)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping.registerHandlerMethod(RequestMappingHandlerMapping.java:74)
	at org.springframework.web.servlet.handler.AbstractHandlerMethodMapping.lambda$detectHandlerMethods$1(AbstractHandlerMethodMapping.java:288)
	at java.base/java.util.LinkedHashMap.forEach(LinkedHashMap.java:684)
	at org.springframework.web.servlet.handler.AbstractHandlerMethodMapping.detectHandlerMethods(AbstractHandlerMethodMapping.java:286)
	at org.springframework.web.servlet.handler.AbstractHandlerMethodMapping.processCandidateBean(AbstractHandlerMethodMapping.java:258)
	at org.springframework.web.servlet.handler.AbstractHandlerMethodMapping.initHandlerMethods(AbstractHandlerMethodMapping.java:217)
	at org.springframework.web.servlet.handler.AbstractHandlerMethodMapping.afterPropertiesSet(AbstractHandlerMethodMapping.java:205)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping.afterPropertiesSet(RequestMappingHandlerMapping.java:188)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1855)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1792)
	... 22 common frames omitted

[wilkinsona]

Thanks for the report. There are two parts to it.

The first is somewhat similar to spring-projects/spring-framework#25050. It's not clear from the output shared above, but I think this is being reported by FailureAnalyzers via debug logging and, while ugly, isn't causing a failure. It seems valid for java.lang.TypeNotPresentException to be thrown by the call to java.lang.Class.getGenericSuperclass from ResolvableType. I've opened spring-projects/spring-framework#25064 to see if Framework can handle the exception.

The second is that the suspending handler method has been identified as one that is unsupported. The stack suggests that you are using Spring MVC rather than Spring WebFlux which contradicts the dependencies you've listed. So that we can be certain of what's happening in your app, can you please provide a minimal sample that reproduces the problem you have described? You can do so by zipping it up and attaching it to this issue or by pushing it to a separate repository on GitHub.

[MikeMitterer]

Thanks! It's in the sbsuspend-branch: https://github.com/MikeMitterer/kotlin-catshostel-sb/tree/sbsuspend

[wilkinsona]

Thanks for the link to the app.

As suspected, the problem is that you are using Spring MVC rather than Spring WebFlux. Unlike WebFlux, MVC does not support suspending handler methods. You are using MVC because of your dependency on spring-boot-starter-websocket which pulls in spring-boot-starter-web.

WebFlux's WebSocket support (part of the spring-webflux module) isn't a drop in replacement for WebSocket support that's part of spring-websocket. If you want to use WebFlux with your app, you'll have to rewrite the WebSocket-related parts of it.

If you have any further questions, please follow up on Stack Overflow or Gitter. As mentioned in the guidelines for contributing, we prefer to use GitHub issues only for bugs and enhancements.