Spring Expression Language (SpEL)

The Spring Expression Language (“SpEL” for short) is a powerful expression language that supports querying and manipulating an object graph at runtime. The language syntax is similar to Unified EL but offers additional features, most notably method invocation and basic string templating functionality.

While there are several other Java expression languages available — OGNL, MVEL, and JBoss EL, to name a few — the Spring Expression Language was created to provide the Spring community with a single well supported expression language that can be used across all the products in the Spring portfolio. Its language features are driven by the requirements of the projects in the Spring portfolio, including tooling requirements for code completion support within the Spring Tools for Eclipse. That said, SpEL is based on a technology-agnostic API that lets other expression language implementations be integrated, should the need arise.

While SpEL serves as the foundation for expression evaluation within the Spring portfolio, it is not directly tied to Spring and can be used independently. To be self contained, many of the examples in this chapter use SpEL as if it were an independent expression language. This requires creating a few bootstrapping infrastructure classes, such as the parser. Most Spring users need not deal with this infrastructure and can, instead, author only expression strings for evaluation. An example of this typical use is the integration of SpEL into creating XML or annotation-based bean definitions, as shown in Expression support for defining bean definitions.

This chapter covers the features of the expression language, its API, and its language syntax. In several places, Inventor and Society classes are used as the target objects for expression evaluation. These class declarations and the data used to populate them are listed at the end of the chapter.

The expression language supports the following functionality:

Literal expressions
Boolean and relational operators
Regular expressions
Class expressions
Accessing properties, arrays, lists, and maps
Method invocation
Relational operators
Assignment
Calling constructors
Bean references
Array construction
Inline lists
Inline maps
Ternary operator
Variables
User-defined functions
Collection projection
Collection selection
Templated expressions

Evaluation

This section introduces the simple use of SpEL interfaces and its expression language. The complete language reference can be found in Language Reference.

The following code introduces the SpEL API to evaluate the literal string expression, Hello World.

Java

ExpressionParser parser = new SpelExpressionParser();
Expression exp = parser.parseExpression("'Hello World'"); // (1)
String message = (String) exp.getValue();

The value of the message variable is 'Hello World'.

Kotlin

val parser = SpelExpressionParser()
val exp = parser.parseExpression("'Hello World'") // (1)
val message = exp.value as String

The value of the message variable is 'Hello World'.

The SpEL classes and interfaces you are most likely to use are located in the org.springframework.expression package and its sub-packages, such as spel.support.

The ExpressionParser interface is responsible for parsing an expression string. In the preceding example, the expression string is a string literal denoted by the surrounding single quotation marks. The Expression interface is responsible for evaluating the previously defined expression string. Two exceptions that can be thrown, ParseException and EvaluationException, when calling parser.parseExpression and exp.getValue, respectively.

SpEL supports a wide range of features, such as calling methods, accessing properties, and calling constructors.

In the following example of method invocation, we call the concat method on the string literal:

Java

ExpressionParser parser = new SpelExpressionParser();
Expression exp = parser.parseExpression("'Hello World'.concat('!')"); // (1)
String message = (String) exp.getValue();

The value of message is now 'Hello World!'.

Kotlin

val parser = SpelExpressionParser()
val exp = parser.parseExpression("'Hello World'.concat('!')") // (1)
val message = exp.value as String

The value of message is now 'Hello World!'.

The following example of calling a JavaBean property calls the String property Bytes:

Java

ExpressionParser parser = new SpelExpressionParser();

// invokes 'getBytes()'
Expression exp = parser.parseExpression("'Hello World'.bytes"); // (1)
byte[] bytes = (byte[]) exp.getValue();

This line converts the literal to a byte array.

Kotlin

val parser = SpelExpressionParser()

// invokes 'getBytes()'
val exp = parser.parseExpression("'Hello World'.bytes") // (1)
val bytes = exp.value as ByteArray

This line converts the literal to a byte array.

SpEL also supports nested properties by using the standard dot notation (such as prop1.prop2.prop3) and also the corresponding setting of property values. Public fields may also be accessed.

The following example shows how to use dot notation to get the length of a literal:

Java

ExpressionParser parser = new SpelExpressionParser();

// invokes 'getBytes().length'
Expression exp = parser.parseExpression("'Hello World'.bytes.length"); // (1)
int length = (Integer) exp.getValue();

'Hello World'.bytes.length gives the length of the literal.

Kotlin

val parser = SpelExpressionParser()

// invokes 'getBytes().length'
val exp = parser.parseExpression("'Hello World'.bytes.length") // (1)
val length = exp.value as Int

'Hello World'.bytes.length gives the length of the literal.

The String’s constructor can be called instead of using a string literal, as the following example shows:

Java

ExpressionParser parser = new SpelExpressionParser();
Expression exp = parser.parseExpression("new String('hello world').toUpperCase()"); // (1)
String message = exp.getValue(String.class);

Construct a new String from the literal and make it be upper case.

Kotlin

val parser = SpelExpressionParser()
val exp = parser.parseExpression("new String('hello world').toUpperCase()")  // (1)
val message = exp.getValue(String::class.java)

Construct a new String from the literal and make it be upper case.

Note the use of the generic method: public <T> T getValue(Class<T> desiredResultType). Using this method removes the need to cast the value of the expression to the desired result type. An EvaluationException is thrown if the value cannot be cast to the type T or converted by using the registered type converter.

The more common usage of SpEL is to provide an expression string that is evaluated against a specific object instance (called the root object). The following example shows how to retrieve the name property from an instance of the Inventor class or create a boolean condition:

Java

// Create and set a calendar
GregorianCalendar c = new GregorianCalendar();
c.set(1856, 7, 9);

// The constructor arguments are name, birthday, and nationality.
Inventor tesla = new Inventor("Nikola Tesla", c.getTime(), "Serbian");

ExpressionParser parser = new SpelExpressionParser();

Expression exp = parser.parseExpression("name"); // Parse name as an expression
String name = (String) exp.getValue(tesla);
// name == "Nikola Tesla"

exp = parser.parseExpression("name == 'Nikola Tesla'");
boolean result = exp.getValue(tesla, Boolean.class);
// result == true

Kotlin

// Create and set a calendar
val c = GregorianCalendar()
c.set(1856, 7, 9)

// The constructor arguments are name, birthday, and nationality.
val tesla = Inventor("Nikola Tesla", c.time, "Serbian")

val parser = SpelExpressionParser()

var exp = parser.parseExpression("name") // Parse name as an expression
val name = exp.getValue(tesla) as String
// name == "Nikola Tesla"

exp = parser.parseExpression("name == 'Nikola Tesla'")
val result = exp.getValue(tesla, Boolean::class.java)
// result == true

Understanding `EvaluationContext`

The EvaluationContext interface is used when evaluating an expression to resolve properties, methods, or fields and to help perform type conversion. Spring provides two implementations.

SimpleEvaluationContext: Exposes a subset of essential SpEL language features and configuration options, for categories of expressions that do not require the full extent of the SpEL language syntax and should be meaningfully restricted. Examples include but are not limited to data binding expressions and property-based filters.
StandardEvaluationContext: Exposes the full set of SpEL language features and configuration options. You can use it to specify a default root object and to configure every available evaluation-related strategy.

SimpleEvaluationContext is designed to support only a subset of the SpEL language syntax. It excludes Java type references, constructors, and bean references. It also requires you to explicitly choose the level of support for properties and methods in expressions. By default, the create() static factory method enables only read access to properties. You can also obtain a builder to configure the exact level of support needed, targeting one or some combination of the following:

Custom PropertyAccessor only (no reflection)
Data binding properties for read-only access
Data binding properties for read and write

Type Conversion

By default, SpEL uses the conversion service available in Spring core (org.springframework.core.convert.ConversionService). This conversion service comes with many built-in converters for common conversions but is also fully extensible so that you can add custom conversions between types. Additionally, it is generics-aware. This means that, when you work with generic types in expressions, SpEL attempts conversions to maintain type correctness for any objects it encounters.

What does this mean in practice? Suppose assignment, using setValue(), is being used to set a List property. The type of the property is actually List<Boolean>. SpEL recognizes that the elements of the list need to be converted to Boolean before being placed in it. The following example shows how to do so:

Java

class Simple {
	public List<Boolean> booleanList = new ArrayList<Boolean>();
}

Simple simple = new Simple();
simple.booleanList.add(true);

EvaluationContext context = SimpleEvaluationContext.forReadOnlyDataBinding().build();

// "false" is passed in here as a String. SpEL and the conversion service
// will recognize that it needs to be a Boolean and convert it accordingly.
parser.parseExpression("booleanList[0]").setValue(context, simple, "false");

// b is false
Boolean b = simple.booleanList.get(0);

Kotlin

class Simple {
	var booleanList: MutableList<Boolean> = ArrayList()
}

val simple = Simple()
simple.booleanList.add(true)

val context = SimpleEvaluationContext.forReadOnlyDataBinding().build()

// "false" is passed in here as a String. SpEL and the conversion service
// will recognize that it needs to be a Boolean and convert it accordingly.
parser.parseExpression("booleanList[0]").setValue(context, simple, "false")

// b is false
val b = simple.booleanList[0]

Parser Configuration

It is possible to configure the SpEL expression parser by using a parser configuration object (org.springframework.expression.spel.SpelParserConfiguration). The configuration object controls the behavior of some of the expression components. For example, if you index into an array or collection and the element at the specified index is null, you can automatically create the element. This is useful when using expressions made up of a chain of property references. If you index into an array or list and specifying an index that is beyond the end of the current size of the array or list, you can automatically grow the array or list to accommodate that index. The following example demonstrates how to automatically grow the list:

Java

class Demo {
	public List<String> list;
}

// Turn on:
// - auto null reference initialization
// - auto collection growing
SpelParserConfiguration config = new SpelParserConfiguration(true,true);

ExpressionParser parser = new SpelExpressionParser(config);

Expression expression = parser.parseExpression("list[3]");

Demo demo = new Demo();

Object o = expression.getValue(demo);

// demo.list will now be a real collection of 4 entries
// Each entry is a new empty String

Kotlin

class Demo {
	var list: List<String>? = null
}

// Turn on:
// - auto null reference initialization
// - auto collection growing
val config = SpelParserConfiguration(true, true)

val parser = SpelExpressionParser(config)

val expression = parser.parseExpression("list[3]")

val demo = Demo()

val o = expression.getValue(demo)

// demo.list will now be a real collection of 4 entries
// Each entry is a new empty String

SpEL Compilation

Spring Framework 4.1 includes a basic expression compiler. Expressions are usually interpreted, which provides a lot of dynamic flexibility during evaluation but does not provide optimum performance. For occasional expression usage, this is fine, but, when used by other components such as Spring Integration, performance can be very important, and there is no real need for the dynamism.

The SpEL compiler is intended to address this need. During evaluation, the compiler generates a Java class that embodies the expression behavior at runtime and uses that class to achieve much faster expression evaluation. Due to the lack of typing around expressions, the compiler uses information gathered during the interpreted evaluations of an expression when performing compilation. For example, it does not know the type of a property reference purely from the expression, but during the first interpreted evaluation, it finds out what it is. Of course, basing compilation on such derived information can cause trouble later if the types of the various expression elements change over time. For this reason, compilation is best suited to expressions whose type information is not going to change on repeated evaluations.

Consider the following basic expression:

someArray[0].someProperty.someOtherProperty < 0.1

Because the preceding expression involves array access, some property de-referencing, and numeric operations, the performance gain can be very noticeable. In an example micro benchmark run of 50000 iterations, it took 75ms to evaluate by using the interpreter and only 3ms using the compiled version of the expression.

Compiler Configuration

The compiler is not turned on by default, but you can turn it on in either of two different ways. You can turn it on by using the parser configuration process (discussed earlier) or by using a system property when SpEL usage is embedded inside another component. This section discusses both of these options.

The compiler can operate in one of three modes, which are captured in the org.springframework.expression.spel.SpelCompilerMode enum. The modes are as follows:

OFF (default): The compiler is switched off.
IMMEDIATE: In immediate mode, the expressions are compiled as soon as possible. This is typically after the first interpreted evaluation. If the compiled expression fails (typically due to a type changing, as described earlier), the caller of the expression evaluation receives an exception.
MIXED: In mixed mode, the expressions silently switch between interpreted and compiled mode over time. After some number of interpreted runs, they switch to compiled form and, if something goes wrong with the compiled form (such as a type changing, as described earlier), the expression automatically switches back to interpreted form again. Sometime later, it may generate another compiled form and switch to it. Basically, the exception that the user gets in IMMEDIATE mode is instead handled internally.

IMMEDIATE mode exists because MIXED mode could cause issues for expressions that have side effects. If a compiled expression blows up after partially succeeding, it may have already done something that has affected the state of the system. If this has happened, the caller may not want it to silently re-run in interpreted mode, since part of the expression may be running twice.

After selecting a mode, use the SpelParserConfiguration to configure the parser. The following example shows how to do so:

Java

SpelParserConfiguration config = new SpelParserConfiguration(SpelCompilerMode.IMMEDIATE,
	this.getClass().getClassLoader());

SpelExpressionParser parser = new SpelExpressionParser(config);

Expression expr = parser.parseExpression("payload");

MyMessage message = new MyMessage();

Object payload = expr.getValue(message);

Kotlin

val config = SpelParserConfiguration(SpelCompilerMode.IMMEDIATE,
		this.javaClass.classLoader)

val parser = SpelExpressionParser(config)

val expr = parser.parseExpression("payload")

val message = MyMessage()

val payload = expr.getValue(message)

When you specify the compiler mode, you can also specify a classloader (passing null is allowed). Compiled expressions are defined in a child classloader created under any that is supplied. It is important to ensure that, if a classloader is specified, it can see all the types involved in the expression evaluation process. If you do not specify a classloader, a default classloader is used (typically the context classloader for the thread that is running during expression evaluation).

The second way to configure the compiler is for use when SpEL is embedded inside some other component and it may not be possible to configure it through a configuration object. In these cases, it is possible to use a system property. You can set the spring.expression.compiler.mode property to one of the SpelCompilerMode enum values (off, immediate, or mixed).

Compiler Limitations

Since Spring Framework 4.1, the basic compilation framework is in place. However, the framework does not yet support compiling every kind of expression. The initial focus has been on the common expressions that are likely to be used in performance-critical contexts. The following kinds of expression cannot be compiled at the moment:

Expressions involving assignment
Expressions relying on the conversion service
Expressions using custom resolvers or accessors
Expressions using selection or projection

More types of expression will be compilable in the future.

Expressions in Bean Definitions

You can use SpEL expressions with XML-based or annotation-based configuration metadata for defining BeanDefinition instances. In both cases, the syntax to define the expression is of the form #{ <expression string> }.

XML Configuration

A property or constructor argument value can be set by using expressions, as the following example shows:

<bean id="numberGuess" class="org.spring.samples.NumberGuess">
	<property name="randomNumber" value="#{ T(java.lang.Math).random() * 100.0 }"/>

	<!-- other properties -->
</bean>

All beans in the application context are available as predefined variables with their common bean name. This includes standard context beans such as environment (of type org.springframework.core.env.Environment) as well as systemProperties and systemEnvironment (of type Map<String, Object>) for access to the runtime environment.

The following example shows access to the systemProperties bean as a SpEL variable:

<bean id="taxCalculator" class="org.spring.samples.TaxCalculator">
	<property name="defaultLocale" value="#{ systemProperties['user.region'] }"/>

	<!-- other properties -->
</bean>

Note that you do not have to prefix the predefined variable with the # symbol here.

You can also refer to other bean properties by name, as the following example shows:

<bean id="numberGuess" class="org.spring.samples.NumberGuess">
	<property name="randomNumber" value="#{ T(java.lang.Math).random() * 100.0 }"/>

	<!-- other properties -->
</bean>

<bean id="shapeGuess" class="org.spring.samples.ShapeGuess">
	<property name="initialShapeSeed" value="#{ numberGuess.randomNumber }"/>

	<!-- other properties -->
</bean>

Annotation Configuration

To specify a default value, you can place the @Value annotation on fields, methods, and method or constructor parameters.

The following example sets the default value of a field variable:

Java

public class FieldValueTestBean {

	@Value("#{ systemProperties['user.region'] }")
	private String defaultLocale;

	public void setDefaultLocale(String defaultLocale) {
		this.defaultLocale = defaultLocale;
	}

	public String getDefaultLocale() {
		return this.defaultLocale;
	}
}

Kotlin

class FieldValueTestBean {

	@Value("#{ systemProperties['user.region'] }")
	var defaultLocale: String? = null
}

The following example shows the equivalent but on a property setter method:

Java

public class PropertyValueTestBean {

	private String defaultLocale;

	@Value("#{ systemProperties['user.region'] }")
	public void setDefaultLocale(String defaultLocale) {
		this.defaultLocale = defaultLocale;
	}

	public String getDefaultLocale() {
		return this.defaultLocale;
	}
}

Kotlin

class PropertyValueTestBean {

	@Value("#{ systemProperties['user.region'] }")
	var defaultLocale: String? = null
}

Autowired methods and constructors can also use the @Value annotation, as the following examples show:

Java

public class SimpleMovieLister {

	private MovieFinder movieFinder;
	private String defaultLocale;

	@Autowired
	public void configure(MovieFinder movieFinder,
			@Value("#{ systemProperties['user.region'] }") String defaultLocale) {
		this.movieFinder = movieFinder;
		this.defaultLocale = defaultLocale;
	}

	// ...
}

Kotlin

class SimpleMovieLister {

	private lateinit var movieFinder: MovieFinder
	private lateinit var defaultLocale: String

	@Autowired
	fun configure(movieFinder: MovieFinder,
				@Value("#{ systemProperties['user.region'] }") defaultLocale: String) {
		this.movieFinder = movieFinder
		this.defaultLocale = defaultLocale
	}

	// ...
}

Java

public class MovieRecommender {

	private String defaultLocale;

	private CustomerPreferenceDao customerPreferenceDao;

	public MovieRecommender(CustomerPreferenceDao customerPreferenceDao,
			@Value("#{systemProperties['user.country']}") String defaultLocale) {
		this.customerPreferenceDao = customerPreferenceDao;
		this.defaultLocale = defaultLocale;
	}

	// ...
}

Kotlin

class MovieRecommender(private val customerPreferenceDao: CustomerPreferenceDao,
			@Value("#{systemProperties['user.country']}") private val defaultLocale: String) {
	// ...
}

Language Reference

This section describes how the Spring Expression Language works. It covers the following topics:

Literal Expressions
Properties, Arrays, Lists, Maps, and Indexers
Inline Lists
Inline Maps
Array Construction
Methods
Operators
Types
Constructors
Variables
Functions
Bean References
Ternary Operator (If-Then-Else)
The Elvis Operator
Safe Navigation Operator

Literal Expressions

The types of literal expressions supported are strings, numeric values (int, real, hex), boolean, and null. Strings are delimited by single quotation marks. To put a single quotation mark itself in a string, use two single quotation mark characters.

The following listing shows simple usage of literals. Typically, they are not used in isolation like this but, rather, as part of a more complex expression — for example, using a literal on one side of a logical comparison operator.

Java

ExpressionParser parser = new SpelExpressionParser();

// evals to "Hello World"
String helloWorld = (String) parser.parseExpression("'Hello World'").getValue();

double avogadrosNumber = (Double) parser.parseExpression("6.0221415E+23").getValue();

// evals to 2147483647
int maxValue = (Integer) parser.parseExpression("0x7FFFFFFF").getValue();

boolean trueValue = (Boolean) parser.parseExpression("true").getValue();

Object nullValue = parser.parseExpression("null").getValue();

Kotlin

val parser = SpelExpressionParser()

// evals to "Hello World"
val helloWorld = parser.parseExpression("'Hello World'").value as String

val avogadrosNumber = parser.parseExpression("6.0221415E+23").value as Double

// evals to 2147483647
val maxValue = parser.parseExpression("0x7FFFFFFF").value as Int

val trueValue = parser.parseExpression("true").value as Boolean

val nullValue = parser.parseExpression("null").value

Numbers support the use of the negative sign, exponential notation, and decimal points. By default, real numbers are parsed by using Double.parseDouble().

Properties, Arrays, Lists, Maps, and Indexers

Navigating with property references is easy. To do so, use a period to indicate a nested property value. The instances of the Inventor class, pupin and tesla, were populated with data listed in the Classes used in the examples section. To navigate “down” and get Tesla’s year of birth and Pupin’s city of birth, we use the following expressions:

Java

// evals to 1856
int year = (Integer) parser.parseExpression("Birthdate.Year + 1900").getValue(context);

String city = (String) parser.parseExpression("placeOfBirth.City").getValue(context);

Kotlin

// evals to 1856
val year = parser.parseExpression("Birthdate.Year + 1900").getValue(context) as Int

val city = parser.parseExpression("placeOfBirth.City").getValue(context) as String

Case insensitivity is allowed for the first letter of property names. The contents of arrays and lists are obtained by using square bracket notation, as the following example shows:

Java

ExpressionParser parser = new SpelExpressionParser();
EvaluationContext context = SimpleEvaluationContext.forReadOnlyDataBinding().build();

// Inventions Array

// evaluates to "Induction motor"
String invention = parser.parseExpression("inventions[3]").getValue(
		context, tesla, String.class);

// Members List

// evaluates to "Nikola Tesla"
String name = parser.parseExpression("Members[0].Name").getValue(
		context, ieee, String.class);

// List and Array navigation
// evaluates to "Wireless communication"
String invention = parser.parseExpression("Members[0].Inventions[6]").getValue(
		context, ieee, String.class);

Kotlin

val parser = SpelExpressionParser()
val context = SimpleEvaluationContext.forReadOnlyDataBinding().build()

// Inventions Array

// evaluates to "Induction motor"
val invention = parser.parseExpression("inventions[3]").getValue(
		context, tesla, String::class.java)

// Members List

// evaluates to "Nikola Tesla"
val name = parser.parseExpression("Members[0].Name").getValue(
		context, ieee, String::class.java)

// List and Array navigation
// evaluates to "Wireless communication"
val invention = parser.parseExpression("Members[0].Inventions[6]").getValue(
		context, ieee, String::class.java)

The contents of maps are obtained by specifying the literal key value within the brackets. In the following example, because keys for the Officers map are strings, we can specify string literals:

Java

// Officer's Dictionary

Inventor pupin = parser.parseExpression("Officers['president']").getValue(
		societyContext, Inventor.class);

// evaluates to "Idvor"
String city = parser.parseExpression("Officers['president'].PlaceOfBirth.City").getValue(
		societyContext, String.class);

// setting values
parser.parseExpression("Officers['advisors'][0].PlaceOfBirth.Country").setValue(
		societyContext, "Croatia");

Kotlin

// Officer's Dictionary

val pupin = parser.parseExpression("Officers['president']").getValue(
		societyContext, Inventor::class.java)

// evaluates to "Idvor"
val city = parser.parseExpression("Officers['president'].PlaceOfBirth.City").getValue(
		societyContext, String::class.java)

// setting values
parser.parseExpression("Officers['advisors'][0].PlaceOfBirth.Country").setValue(
		societyContext, "Croatia")

Inline Lists

You can directly express lists in an expression by using {} notation.

Java

// evaluates to a Java list containing the four numbers
List numbers = (List) parser.parseExpression("{1,2,3,4}").getValue(context);

List listOfLists = (List) parser.parseExpression("{{'a','b'},{'x','y'}}").getValue(context);

Kotlin

// evaluates to a Java list containing the four numbers
val numbers = parser.parseExpression("{1,2,3,4}").getValue(context) as List<*>

val listOfLists = parser.parseExpression("{{'a','b'},{'x','y'}}").getValue(context) as List<*>

{} by itself means an empty list. For performance reasons, if the list is itself entirely composed of fixed literals, a constant list is created to represent the expression (rather than building a new list on each evaluation).

Inline Maps

You can also directly express maps in an expression by using {key:value} notation. The following example shows how to do so:

Java

// evaluates to a Java map containing the two entries
Map inventorInfo = (Map) parser.parseExpression("{name:'Nikola',dob:'10-July-1856'}").getValue(context);

Map mapOfMaps = (Map) parser.parseExpression("{name:{first:'Nikola',last:'Tesla'},dob:{day:10,month:'July',year:1856}}").getValue(context);

Kotlin

// evaluates to a Java map containing the two entries
val inventorInfo = parser.parseExpression("{name:'Nikola',dob:'10-July-1856'}").getValue(context) as Map<*, >

val mapOfMaps = parser.parseExpression("{name:{first:'Nikola',last:'Tesla'},dob:{day:10,month:'July',year:1856}}").getValue(context) as Map<, *>

{:} by itself means an empty map. For performance reasons, if the map is itself composed of fixed literals or other nested constant structures (lists or maps), a constant map is created to represent the expression (rather than building a new map on each evaluation). Quoting of the map keys is optional. The examples above do not use quoted keys.

Array Construction

You can build arrays by using the familiar Java syntax, optionally supplying an initializer to have the array populated at construction time. The following example shows how to do so:

Java

int[] numbers1 = (int[]) parser.parseExpression("new int[4]").getValue(context);

// Array with initializer
int[] numbers2 = (int[]) parser.parseExpression("new int[]{1,2,3}").getValue(context);

// Multi dimensional array
int[][] numbers3 = (int[][]) parser.parseExpression("new int[4][5]").getValue(context);

Kotlin

val numbers1 = parser.parseExpression("new int[4]").getValue(context) as IntArray

// Array with initializer
val numbers2 = parser.parseExpression("new int[]{1,2,3}").getValue(context) as IntArray

// Multi dimensional array
val numbers3 = parser.parseExpression("new int[4][5]").getValue(context) as Array<IntArray>

You cannot currently supply an initializer when you construct multi-dimensional array.

Methods

You can invoke methods by using typical Java programming syntax. You can also invoke methods on literals. Variable arguments are also supported. The following examples show how to invoke methods:

Java

// string literal, evaluates to "bc"
String bc = parser.parseExpression("'abc'.substring(1, 3)").getValue(String.class);

// evaluates to true
boolean isMember = parser.parseExpression("isMember('Mihajlo Pupin')").getValue(
		societyContext, Boolean.class);

Kotlin

// string literal, evaluates to "bc"
val bc = parser.parseExpression("'abc'.substring(1, 3)").getValue(String::class.java)

// evaluates to true
val isMember = parser.parseExpression("isMember('Mihajlo Pupin')").getValue(
		societyContext, Boolean::class.java)

Operators

The Spring Expression Language supports the following kinds of operators:

Relational Operators
Logical Operators
Mathematical Operators
The Assignment Operator

Relational Operators

The relational operators (equal, not equal, less than, less than or equal, greater than, and greater than or equal) are supported by using standard operator notation. The following listing shows a few examples of operators:

Java

// evaluates to true
boolean trueValue = parser.parseExpression("2 == 2").getValue(Boolean.class);

// evaluates to false
boolean falseValue = parser.parseExpression("2 < -5.0").getValue(Boolean.class);

// evaluates to true
boolean trueValue = parser.parseExpression("'black' < 'block'").getValue(Boolean.class);

Kotlin

// evaluates to true
val trueValue = parser.parseExpression("2 == 2").getValue(Boolean::class.java)

// evaluates to false
val falseValue = parser.parseExpression("2 < -5.0").getValue(Boolean::class.java)

// evaluates to true
val trueValue = parser.parseExpression("'black' < 'block'").getValue(Boolean::class.java)

Note

Greater-than and less-than comparisons against null follow a simple rule: null is treated as nothing (that is NOT as zero). As a consequence, any other value is always greater than null (X > null is always true) and no other value is ever less than nothing (X < null is always false).

If you prefer numeric comparisons instead, avoid number-based null comparisons in favor of comparisons against zero (for example, X > 0 or X < 0).

In addition to the standard relational operators, SpEL supports the instanceof and regular expression-based matches operator. The following listing shows examples of both:

Java

// evaluates to false
boolean falseValue = parser.parseExpression(
		"'xyz' instanceof T(Integer)").getValue(Boolean.class);

// evaluates to true
boolean trueValue = parser.parseExpression(
		"'5.00' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean.class);

//evaluates to false
boolean falseValue = parser.parseExpression(
		"'5.0067' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean.class);

Kotlin

// evaluates to false
val falseValue = parser.parseExpression(
		"'xyz' instanceof T(Integer)").getValue(Boolean::class.java)

// evaluates to true
val trueValue = parser.parseExpression(
		"'5.00' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean::class.java)

//evaluates to false
val falseValue = parser.parseExpression(
		"'5.0067' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean::class.java)

Caution

Be careful with primitive types, as they are immediately boxed up to the wrapper type, so 1 instanceof T(int) evaluates to false while 1 instanceof T(Integer) evaluates to true, as expected.

Each symbolic operator can also be specified as a purely alphabetic equivalent. This avoids problems where the symbols used have special meaning for the document type in which the expression is embedded (such as in an XML document). The textual equivalents are:

lt (<)
gt (>)
le (<=)
ge (>=)
eq (==)
ne (!=)
div (/)
mod (%)
not (!).

All of the textual operators are case-insensitive.

Logical Operators

SpEL supports the following logical operators:

and (&&)
or (||)
not (!)

The following example shows how to use the logical operators

Java

// -- AND --

// evaluates to false
boolean falseValue = parser.parseExpression("true and false").getValue(Boolean.class);

// evaluates to true
String expression = "isMember('Nikola Tesla') and isMember('Mihajlo Pupin')";
boolean trueValue = parser.parseExpression(expression).getValue(societyContext, Boolean.class);

// -- OR --

// evaluates to true
boolean trueValue = parser.parseExpression("true or false").getValue(Boolean.class);

// evaluates to true
String expression = "isMember('Nikola Tesla') or isMember('Albert Einstein')";
boolean trueValue = parser.parseExpression(expression).getValue(societyContext, Boolean.class);

// -- NOT --

// evaluates to false
boolean falseValue = parser.parseExpression("!true").getValue(Boolean.class);

// -- AND and NOT --
String expression = "isMember('Nikola Tesla') and !isMember('Mihajlo Pupin')";
boolean falseValue = parser.parseExpression(expression).getValue(societyContext, Boolean.class);

Kotlin

// -- AND --

// evaluates to false
val falseValue = parser.parseExpression("true and false").getValue(Boolean::class.java)

// evaluates to true
val expression = "isMember('Nikola Tesla') and isMember('Mihajlo Pupin')"
val trueValue = parser.parseExpression(expression).getValue(societyContext, Boolean::class.java)

// -- OR --

// evaluates to true
val trueValue = parser.parseExpression("true or false").getValue(Boolean::class.java)

// evaluates to true
val expression = "isMember('Nikola Tesla') or isMember('Albert Einstein')"
val trueValue = parser.parseExpression(expression).getValue(societyContext, Boolean::class.java)

// -- NOT --

// evaluates to false
val falseValue = parser.parseExpression("!true").getValue(Boolean::class.java)

// -- AND and NOT --
val expression = "isMember('Nikola Tesla') and !isMember('Mihajlo Pupin')"
val falseValue = parser.parseExpression(expression).getValue(societyContext, Boolean::class.java)

Mathematical Operators

You can use the addition operator on both numbers and strings. You can use the subtraction, multiplication, and division operators only on numbers. You can also use the modulus (%) and exponential power (^) operators. Standard operator precedence is enforced. The following example shows the mathematical operators in use:

Java

// Addition
int two = parser.parseExpression("1 + 1").getValue(Integer.class);  // 2

String testString = parser.parseExpression(
		"'test' + ' ' + 'string'").getValue(String.class);  // 'test string'

// Subtraction
int four = parser.parseExpression("1 - -3").getValue(Integer.class);  // 4

double d = parser.parseExpression("1000.00 - 1e4").getValue(Double.class);  // -9000

// Multiplication
int six = parser.parseExpression("-2 * -3").getValue(Integer.class);  // 6

double twentyFour = parser.parseExpression("2.0 * 3e0 * 4").getValue(Double.class);  // 24.0

// Division
int minusTwo = parser.parseExpression("6 / -3").getValue(Integer.class);  // -2

double one = parser.parseExpression("8.0 / 4e0 / 2").getValue(Double.class);  // 1.0

// Modulus
int three = parser.parseExpression("7 % 4").getValue(Integer.class);  // 3

int one = parser.parseExpression("8 / 5 % 2").getValue(Integer.class);  // 1

// Operator precedence
int minusTwentyOne = parser.parseExpression("1+2-3*8").getValue(Integer.class);  // -21

Kotlin

// Addition
val two = parser.parseExpression("1 + 1").getValue(Int::class.java)  // 2

val testString = parser.parseExpression(
		"'test' + ' ' + 'string'").getValue(String::class.java)  // 'test string'

// Subtraction
val four = parser.parseExpression("1 - -3").getValue(Int::class.java)  // 4

val d = parser.parseExpression("1000.00 - 1e4").getValue(Double::class.java)  // -9000

// Multiplication
val six = parser.parseExpression("-2 * -3").getValue(Int::class.java)  // 6

val twentyFour = parser.parseExpression("2.0 * 3e0 * 4").getValue(Double::class.java)  // 24.0

// Division
val minusTwo = parser.parseExpression("6 / -3").getValue(Int::class.java)  // -2

val one = parser.parseExpression("8.0 / 4e0 / 2").getValue(Double::class.java)  // 1.0

// Modulus
val three = parser.parseExpression("7 % 4").getValue(Int::class.java)  // 3

val one = parser.parseExpression("8 / 5 % 2").getValue(Int::class.java)  // 1

// Operator precedence
val minusTwentyOne = parser.parseExpression("1+2-3*8").getValue(Int::class.java)  // -21

The Assignment Operator

To setting a property, use the assignment operator (=). This is typically done within a call to setValue but can also be done inside a call to getValue. The following listing shows both ways to use the assignment operator:

Java

Inventor inventor = new Inventor();
EvaluationContext context = SimpleEvaluationContext.forReadWriteDataBinding().build();

parser.parseExpression("Name").setValue(context, inventor, "Aleksandar Seovic");

// alternatively
String aleks = parser.parseExpression(
		"Name = 'Aleksandar Seovic'").getValue(context, inventor, String.class);

Kotlin

val inventor = Inventor()
val context = SimpleEvaluationContext.forReadWriteDataBinding().build()

parser.parseExpression("Name").setValue(context, inventor, "Aleksandar Seovic")

// alternatively
val aleks = parser.parseExpression(
		"Name = 'Aleksandar Seovic'").getValue(context, inventor, String::class.java)

Types

You can use the special T operator to specify an instance of java.lang.Class (the type). Static methods are invoked by using this operator as well. The StandardEvaluationContext uses a TypeLocator to find types, and the StandardTypeLocator (which can be replaced) is built with an understanding of the java.lang package. This means that T() references to types within java.lang do not need to be fully qualified, but all other type references must be. The following example shows how to use the T operator:

Java

Class dateClass = parser.parseExpression("T(java.util.Date)").getValue(Class.class);

Class stringClass = parser.parseExpression("T(String)").getValue(Class.class);

boolean trueValue = parser.parseExpression(
		"T(java.math.RoundingMode).CEILING < T(java.math.RoundingMode).FLOOR")
		.getValue(Boolean.class);

Kotlin

val dateClass = parser.parseExpression("T(java.util.Date)").getValue(Class::class.java)

val stringClass = parser.parseExpression("T(String)").getValue(Class::class.java)

val trueValue = parser.parseExpression(
		"T(java.math.RoundingMode).CEILING < T(java.math.RoundingMode).FLOOR")
		.getValue(Boolean::class.java)

Constructors

You can invoke constructors by using the new operator. You should use the fully qualified class name for all but the primitive types (int, float, and so on) and String. The following example shows how to use the new operator to invoke constructors:

Java

Inventor einstein = p.parseExpression(
		"new org.spring.samples.spel.inventor.Inventor('Albert Einstein', 'German')")
		.getValue(Inventor.class);

//create new inventor instance within add method of List
p.parseExpression(
		"Members.add(new org.spring.samples.spel.inventor.Inventor(
			'Albert Einstein', 'German'))").getValue(societyContext);

Kotlin

val einstein = p.parseExpression(
		"new org.spring.samples.spel.inventor.Inventor('Albert Einstein', 'German')")
		.getValue(Inventor::class.java)

//create new inventor instance within add method of List
p.parseExpression(
		"Members.add(new org.spring.samples.spel.inventor.Inventor('Albert Einstein', 'German'))")
		.getValue(societyContext)

Variables

You can reference variables in the expression by using the #variableName syntax. Variables are set by using the setVariable method on EvaluationContext implementations.

Note	Valid variable names must be composed of one or more of the following supported characters. letters: `A` to `Z` and `a` to `z` digits: `0` to `9` underscore: `_` dollar sign: `$`

The following example shows how to use variables.

Java

Inventor tesla = new Inventor("Nikola Tesla", "Serbian");

EvaluationContext context = SimpleEvaluationContext.forReadWriteDataBinding().build();
context.setVariable("newName", "Mike Tesla");

parser.parseExpression("Name = #newName").getValue(context, tesla);
System.out.println(tesla.getName())  // "Mike Tesla"

Kotlin

val tesla = Inventor("Nikola Tesla", "Serbian")

val context = SimpleEvaluationContext.forReadWriteDataBinding().build()
context.setVariable("newName", "Mike Tesla")

parser.parseExpression("Name = #newName").getValue(context, tesla)
println(tesla.name)  // "Mike Tesla"

The `#this` and `#root` Variables

The #this variable is always defined and refers to the current evaluation object (against which unqualified references are resolved). The #root variable is always defined and refers to the root context object. Although #this may vary as components of an expression are evaluated, #root always refers to the root. The following examples show how to use the #this and #root variables:

Java

// create an array of integers
List<Integer> primes = new ArrayList<Integer>();
primes.addAll(Arrays.asList(2,3,5,7,11,13,17));

// create parser and set variable 'primes' as the array of integers
ExpressionParser parser = new SpelExpressionParser();
EvaluationContext context = SimpleEvaluationContext.forReadOnlyDataAccess();
context.setVariable("primes", primes);

// all prime numbers > 10 from the list (using selection ?{...})
// evaluates to [11, 13, 17]
List<Integer> primesGreaterThanTen = (List<Integer>) parser.parseExpression(
		"#primes.?[#this>10]").getValue(context);

Kotlin

// create an array of integers
val primes = ArrayList<Int>()
primes.addAll(listOf(2, 3, 5, 7, 11, 13, 17))

// create parser and set variable 'primes' as the array of integers
val parser = SpelExpressionParser()
val context = SimpleEvaluationContext.forReadOnlyDataAccess()
context.setVariable("primes", primes)

// all prime numbers > 10 from the list (using selection ?{...})
// evaluates to [11, 13, 17]
val primesGreaterThanTen = parser.parseExpression(
		"#primes.?[#this>10]").getValue(context) as List<Int>

Functions

You can extend SpEL by registering user-defined functions that can be called within the expression string. The function is registered through the EvaluationContext. The following example shows how to register a user-defined function:

Java

Method method = ...;

EvaluationContext context = SimpleEvaluationContext.forReadOnlyDataBinding().build();
context.setVariable("myFunction", method);

Kotlin

val method: Method = ...

val context = SimpleEvaluationContext.forReadOnlyDataBinding().build()
context.setVariable("myFunction", method)

For example, consider the following utility method that reverses a string:

Java

public abstract class StringUtils {

	public static String reverseString(String input) {
		StringBuilder backwards = new StringBuilder(input.length());
		for (int i = 0; i < input.length(); i++) {
			backwards.append(input.charAt(input.length() - 1 - i));
		}
		return backwards.toString();
	}
}

Kotlin

fun reverseString(input: String): String {
	val backwards = StringBuilder(input.length)
	for (i in 0 until input.length) {
		backwards.append(input[input.length - 1 - i])
	}
	return backwards.toString()
}

You can then register and use the preceding method, as the following example shows:

Java

ExpressionParser parser = new SpelExpressionParser();

EvaluationContext context = SimpleEvaluationContext.forReadOnlyDataBinding().build();
context.setVariable("reverseString",
		StringUtils.class.getDeclaredMethod("reverseString", String.class));

String helloWorldReversed = parser.parseExpression(
		"#reverseString('hello')").getValue(context, String.class);

Kotlin

val parser = SpelExpressionParser()

val context = SimpleEvaluationContext.forReadOnlyDataBinding().build()
context.setVariable("reverseString", ::reverseString::javaMethod)

val helloWorldReversed = parser.parseExpression(
		"#reverseString('hello')").getValue(context, String::class.java)

Bean References

If the evaluation context has been configured with a bean resolver, you can look up beans from an expression by using the @ symbol. The following example shows how to do so:

Java

ExpressionParser parser = new SpelExpressionParser();
StandardEvaluationContext context = new StandardEvaluationContext();
context.setBeanResolver(new MyBeanResolver());

// This will end up calling resolve(context,"something") on MyBeanResolver during evaluation
Object bean = parser.parseExpression("@something").getValue(context);

Kotlin

val parser = SpelExpressionParser()
val context = StandardEvaluationContext()
context.setBeanResolver(MyBeanResolver())

// This will end up calling resolve(context,"something") on MyBeanResolver during evaluation
val bean = parser.parseExpression("@something").getValue(context)

To access a factory bean itself, you should instead prefix the bean name with an & symbol. The following example shows how to do so:

Java

ExpressionParser parser = new SpelExpressionParser();
StandardEvaluationContext context = new StandardEvaluationContext();
context.setBeanResolver(new MyBeanResolver());

// This will end up calling resolve(context,"&foo") on MyBeanResolver during evaluation
Object bean = parser.parseExpression("&foo").getValue(context);

Kotlin

val parser = SpelExpressionParser()
val context = StandardEvaluationContext()
context.setBeanResolver(MyBeanResolver())

// This will end up calling resolve(context,"&foo") on MyBeanResolver during evaluation
val bean = parser.parseExpression("&foo").getValue(context)

Ternary Operator (If-Then-Else)

You can use the ternary operator for performing if-then-else conditional logic inside the expression. The following listing shows a minimal example:

Java

String falseString = parser.parseExpression(
		"false ? 'trueExp' : 'falseExp'").getValue(String.class);

Kotlin

val falseString = parser.parseExpression(
		"false ? 'trueExp' : 'falseExp'").getValue(String::class.java)

In this case, the boolean false results in returning the string value 'falseExp'. A more realistic example follows:

Java

parser.parseExpression("Name").setValue(societyContext, "IEEE");
societyContext.setVariable("queryName", "Nikola Tesla");

expression = "isMember(#queryName)? #queryName + ' is a member of the ' " +
		"+ Name + ' Society' : #queryName + ' is not a member of the ' + Name + ' Society'";

String queryResultString = parser.parseExpression(expression)
		.getValue(societyContext, String.class);
// queryResultString = "Nikola Tesla is a member of the IEEE Society"

Kotlin

parser.parseExpression("Name").setValue(societyContext, "IEEE")
societyContext.setVariable("queryName", "Nikola Tesla")

expression = "isMember(#queryName)? #queryName + ' is a member of the ' " + "+ Name + ' Society' : #queryName + ' is not a member of the ' + Name + ' Society'"

val queryResultString = parser.parseExpression(expression)
		.getValue(societyContext, String::class.java)
// queryResultString = "Nikola Tesla is a member of the IEEE Society"

See the next section on the Elvis operator for an even shorter syntax for the ternary operator.

The Elvis Operator

The Elvis operator is a shortening of the ternary operator syntax and is used in the Groovy language. With the ternary operator syntax, you usually have to repeat a variable twice, as the following example shows:

String name = "Elvis Presley";
String displayName = (name != null ? name : "Unknown");

Instead, you can use the Elvis operator (named for the resemblance to Elvis' hair style). The following example shows how to use the Elvis operator:

Java

ExpressionParser parser = new SpelExpressionParser();

String name = parser.parseExpression("name?:'Unknown'").getValue(new Inventor(), String.class);
System.out.println(name);  // 'Unknown'

Kotlin

val parser = SpelExpressionParser()

val name = parser.parseExpression("name?:'Unknown'").getValue(Inventor(), String::class.java)
println(name)  // 'Unknown'

The following listing shows a more complex example:

Java

ExpressionParser parser = new SpelExpressionParser();
EvaluationContext context = SimpleEvaluationContext.forReadOnlyDataBinding().build();

Inventor tesla = new Inventor("Nikola Tesla", "Serbian");
String name = parser.parseExpression("Name?:'Elvis Presley'").getValue(context, tesla, String.class);
System.out.println(name);  // Nikola Tesla

tesla.setName(null);
name = parser.parseExpression("Name?:'Elvis Presley'").getValue(context, tesla, String.class);
System.out.println(name);  // Elvis Presley

Kotlin

val parser = SpelExpressionParser()
val context = SimpleEvaluationContext.forReadOnlyDataBinding().build()

val tesla = Inventor("Nikola Tesla", "Serbian")
var name = parser.parseExpression("Name?:'Elvis Presley'").getValue(context, tesla, String::class.java)
println(name)  // Nikola Tesla

tesla.setName(null)
name = parser.parseExpression("Name?:'Elvis Presley'").getValue(context, tesla, String::class.java)
println(name)  // Elvis Presley

Note	You can use the Elvis operator to apply default values in expressions. The following example shows how to use the Elvis operator in a `@Value` expression: @Value("#{systemProperties['pop3.port'] ?: 25}") This will inject a system property `pop3.port` if it is defined or 25 if not.

Safe Navigation Operator

The safe navigation operator is used to avoid a NullPointerException and comes from the Groovy language. Typically, when you have a reference to an object, you might need to verify that it is not null before accessing methods or properties of the object. To avoid this, the safe navigation operator returns null instead of throwing an exception. The following example shows how to use the safe navigation operator:

Java

ExpressionParser parser = new SpelExpressionParser();
EvaluationContext context = SimpleEvaluationContext.forReadOnlyDataBinding().build();

Inventor tesla = new Inventor("Nikola Tesla", "Serbian");
tesla.setPlaceOfBirth(new PlaceOfBirth("Smiljan"));

String city = parser.parseExpression("PlaceOfBirth?.City").getValue(context, tesla, String.class);
System.out.println(city);  // Smiljan

tesla.setPlaceOfBirth(null);
city = parser.parseExpression("PlaceOfBirth?.City").getValue(context, tesla, String.class);
System.out.println(city);  // null - does not throw NullPointerException!!!

Kotlin

val parser = SpelExpressionParser()
val context = SimpleEvaluationContext.forReadOnlyDataBinding().build()

val tesla = Inventor("Nikola Tesla", "Serbian")
tesla.setPlaceOfBirth(PlaceOfBirth("Smiljan"))

var city = parser.parseExpression("PlaceOfBirth?.City").getValue(context, tesla, String::class.java)
println(city)  // Smiljan

tesla.setPlaceOfBirth(null)
city = parser.parseExpression("PlaceOfBirth?.City").getValue(context, tesla, String::class.java)
println(city)  // null - does not throw NullPointerException!!!

Collection Selection

Selection is a powerful expression language feature that lets you transform a source collection into another collection by selecting from its entries.

Selection uses a syntax of .?[selectionExpression]. It filters the collection and returns a new collection that contain a subset of the original elements. For example, selection lets us easily get a list of Serbian inventors, as the following example shows:

Java

List<Inventor> list = (List<Inventor>) parser.parseExpression(
		"Members.?[Nationality == 'Serbian']").getValue(societyContext);

Kotlin

val list = parser.parseExpression(
		"Members.?[Nationality == 'Serbian']").getValue(societyContext) as List<Inventor>

Selection is possible upon both lists and maps. For a list, the selection criteria is evaluated against each individual list element. Against a map, the selection criteria is evaluated against each map entry (objects of the Java type Map.Entry). Each map entry has its key and value accessible as properties for use in the selection.

The following expression returns a new map that consists of those elements of the original map where the entry value is less than 27:

Java

Map newMap = parser.parseExpression("map.?[value<27]").getValue();

Kotlin

val newMap = parser.parseExpression("map.?[value<27]").getValue()

In addition to returning all the selected elements, you can retrieve only the first or the last value. To obtain the first entry matching the selection, the syntax is .^[selectionExpression]. To obtain the last matching selection, the syntax is .$[selectionExpression].

Collection Projection

Projection lets a collection drive the evaluation of a sub-expression, and the result is a new collection. The syntax for projection is .![projectionExpression]. For example, suppose we have a list of inventors but want the list of cities where they were born. Effectively, we want to evaluate 'placeOfBirth.city' for every entry in the inventor list. The following example uses projection to do so:

Java

// returns ['Smiljan', 'Idvor' ]
List placesOfBirth = (List)parser.parseExpression("Members.![placeOfBirth.city]");

Kotlin

// returns ['Smiljan', 'Idvor' ]
val placesOfBirth = parser.parseExpression("Members.![placeOfBirth.city]") as List<*>

You can also use a map to drive projection and, in this case, the projection expression is evaluated against each entry in the map (represented as a Java Map.Entry). The result of a projection across a map is a list that consists of the evaluation of the projection expression against each map entry.

Expression templating

Expression templates allow mixing literal text with one or more evaluation blocks. Each evaluation block is delimited with prefix and suffix characters that you can define. A common choice is to use #{ } as the delimiters, as the following example shows:

Java

String randomPhrase = parser.parseExpression(
		"random number is #{T(java.lang.Math).random()}",
		new TemplateParserContext()).getValue(String.class);

// evaluates to "random number is 0.7038186818312008"

Kotlin

val randomPhrase = parser.parseExpression(
		"random number is #{T(java.lang.Math).random()}",
		TemplateParserContext()).getValue(String::class.java)

// evaluates to "random number is 0.7038186818312008"

The string is evaluated by concatenating the literal text 'random number is ' with the result of evaluating the expression inside the #{ } delimiter (in this case, the result of calling that random() method). The second argument to the parseExpression() method is of the type ParserContext. The ParserContext interface is used to influence how the expression is parsed in order to support the expression templating functionality. The definition of TemplateParserContext follows:

Java

public class TemplateParserContext implements ParserContext {

	public String getExpressionPrefix() {
		return "#{";
	}

	public String getExpressionSuffix() {
		return "}";
	}

	public boolean isTemplate() {
		return true;
	}
}

Kotlin

class TemplateParserContext : ParserContext {

	override fun getExpressionPrefix(): String {
		return "#{"
	}

	override fun getExpressionSuffix(): String {
		return "}"
	}

	override fun isTemplate(): Boolean {
		return true
	}
}

Classes Used in the Examples

This section lists the classes used in the examples throughout this chapter.

Inventor.Java

package org.spring.samples.spel.inventor;

import java.util.Date;
import java.util.GregorianCalendar;

public class Inventor {

	private String name;
	private String nationality;
	private String[] inventions;
	private Date birthdate;
	private PlaceOfBirth placeOfBirth;

	public Inventor(String name, String nationality) {
		GregorianCalendar c= new GregorianCalendar();
		this.name = name;
		this.nationality = nationality;
		this.birthdate = c.getTime();
	}

	public Inventor(String name, Date birthdate, String nationality) {
		this.name = name;
		this.nationality = nationality;
		this.birthdate = birthdate;
	}

	public Inventor() {
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getNationality() {
		return nationality;
	}

	public void setNationality(String nationality) {
		this.nationality = nationality;
	}

	public Date getBirthdate() {
		return birthdate;
	}

	public void setBirthdate(Date birthdate) {
		this.birthdate = birthdate;
	}

	public PlaceOfBirth getPlaceOfBirth() {
		return placeOfBirth;
	}

	public void setPlaceOfBirth(PlaceOfBirth placeOfBirth) {
		this.placeOfBirth = placeOfBirth;
	}

	public void setInventions(String[] inventions) {
		this.inventions = inventions;
	}

	public String[] getInventions() {
		return inventions;
	}
}

Inventor.kt

class Inventor(
	var name: String,
	var nationality: String,
	var inventions: Array<String>? = null,
	var birthdate: Date =  GregorianCalendar().time,
	var placeOfBirth: PlaceOfBirth? = null)

PlaceOfBirth.java

package org.spring.samples.spel.inventor;

public class PlaceOfBirth {

	private String city;
	private String country;

	public PlaceOfBirth(String city) {
		this.city=city;
	}

	public PlaceOfBirth(String city, String country) {
		this(city);
		this.country = country;
	}

	public String getCity() {
		return city;
	}

	public void setCity(String s) {
		this.city = s;
	}

	public String getCountry() {
		return country;
	}

	public void setCountry(String country) {
		this.country = country;
	}
}

PlaceOfBirth.kt

class PlaceOfBirth(var city: String, var country: String? = null) {

Society.java

package org.spring.samples.spel.inventor;

import java.util.*;

public class Society {

	private String name;

	public static String Advisors = "advisors";
	public static String President = "president";

	private List<Inventor> members = new ArrayList<Inventor>();
	private Map officers = new HashMap();

	public List getMembers() {
		return members;
	}

	public Map getOfficers() {
		return officers;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public boolean isMember(String name) {
		for (Inventor inventor : members) {
			if (inventor.getName().equals(name)) {
				return true;
			}
		}
		return false;
	}
}

Society.kt

package org.spring.samples.spel.inventor

import java.util.*

class Society {

	val Advisors = "advisors"
	val President = "president"

	var name: String? = null

	val members = ArrayList<Inventor>()
	val officers = mapOf<Any, Any>()

	fun isMember(name: String): Boolean {
		for (inventor in members) {
			if (inventor.name == name) {
				return true
			}
		}
		return false
	}
}

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Spring Expression Language (SpEL)

Evaluation

Understanding EvaluationContext

Type Conversion

Parser Configuration

SpEL Compilation

Compiler Configuration

Compiler Limitations

Expressions in Bean Definitions

XML Configuration

Annotation Configuration

Language Reference

Literal Expressions

Properties, Arrays, Lists, Maps, and Indexers

Inline Lists

Inline Maps

Array Construction

Methods

Operators

Relational Operators

Logical Operators

Mathematical Operators

The Assignment Operator

Types

Constructors

Variables

The #this and #root Variables

Functions

Bean References

Ternary Operator (If-Then-Else)

The Elvis Operator

Safe Navigation Operator

Collection Selection

Collection Projection

Expression templating

Classes Used in the Examples

Understanding `EvaluationContext`

The `#this` and `#root` Variables