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>

The systemProperties variable is predefined, so you can use it in your expressions, as the following example shows:

<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 in this context.

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) {
	// ...
}