Expressions in Bean Definitions

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

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.

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

The following example sets the default value of a field:

Java
Kotlin

public class FieldValueTestBean {

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

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

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

class FieldValueTestBean {

	@field:Value("#{ systemProperties['user.region'] }")
	lateinit var defaultLocale: String
}

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

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

Java
Kotlin
Xml

public class PropertyValueTestBean {

	private String defaultLocale;

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

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

class PropertyValueTestBean {

	@set:Value("#{ systemProperties['user.region'] }")
	lateinit var defaultLocale: String
}

<bean id="testBean" class="org.springframework.docs.core.expressions.expressionsbeandef.PropertyValueTestBean">
	<property name="defaultLocale" value="#{ systemProperties['user.region'] }"/>
</bean>

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

Java
Kotlin

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;
	}

	// ...
}

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
Kotlin
Xml

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;
	}

	// ...
}

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

<bean id="testBean" class="org.springframework.docs.core.expressions.expressionsbeandef.MovieRecommender">
	<constructor-arg ref="customerPreferenceDao"/>
	<constructor-arg value="#{ systemProperties['user.country'] }"/>
</bean>

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

Java
Kotlin
Xml

public class ShapeGuess {

	private double initialShapeSeed;

	@Value("#{ numberGuess.randomNumber }")
	public void setInitialShapeSeed(double initialShapeSeed) {
		this.initialShapeSeed = initialShapeSeed;
	}

	public double getInitialShapeSeed() {
		return initialShapeSeed;
	}
}

class ShapeGuess {

	@set:Value("#{ numberGuess.randomNumber }")
	var initialShapeSeed: Double = 0.0
}

<bean id="shapeGuess" class="org.springframework.docs.core.expressions.expressionsbeandef.ShapeGuess">
	<property name="initialShapeSeed" value="#{ numberGuess.randomNumber }"/>
</bean>