Spring Tutorial - Spring Expression Language

Spring 3.0 introduced a powerful expression language known as Spring expression language, or Spring EL.

The Spring Expression Language, available via XML or annotation, is evaluated or executed during the bean creation time.

Spring expression language hello world

In the following code shows how to use Spring Expression Language to inject String, integer and bean into property, both in XML and annotation.

In order to use Spring Expression Language we need to add the following jars dependency to the pom.xml file.

...
    <properties>
    <spring.version>3.0.5.RELEASE</spring.version>
  </properties>
  <dependencies>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-core</artifactId>
      <version>${spring.version}</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>${spring.version}</version>
    </dependency>
  <dependencies>
...

Java Bean

The following code defines two Java beans, later we will use Spring Expression Language to inject values into property in XML and annotation.

Server Java Bean.

package com.java2s.common;

public class Server {

  private Item item;

  private String itemName;

  public Item getItem() {
    return item;
  }

  public void setItem(Item item) {
    this.item = item;
  }

  public String getItemName() {
    return itemName;
  }

  public void setItemName(String itemName) {
    this.itemName = itemName;
  }

  @Override
  public String toString() {
    return "Server [item=" + item + ", itemName=" + itemName + "]";
  }

}

Item Java Bean.

package com.java2s.common;


public class Item {

  private String name;

  private int qty;
  public String getName() {
    return name;
  }
  @Override
  public String toString() {
    return "Item [name=" + name + ", qty=" + qty + "]";
  }
  public int getQty() {
    return qty;
  }
  public void setQty(int qty) {
    this.qty = qty;
  }
  public void setName(String name) {
    this.name = name;
  }
}

Spring EL in XML

The following code shows how to use Spring EL in XML.

First, we defined a Java Bean Item in xml and set its property value. We set the name to have itemA value and set 10 as the qty value.

  <bean id="itemBean" class="com.java2s.common.Item">
    <property name="name" value="itemA" />
    <property name="qty" value="10" />
  </bean>

Then, we created the Server bean in XML by reusing the value from Item Bean.

The Spring Expression Language is enclosed with #{ expression }. The following code references the value from Item bean. It assigns the itemBean to item and itemBean.name to itemName. Value of itemBean.name is itemA.

  <bean id="myServer" class="com.java2s.common.Server">
    <property name="item" value="#{itemBean}" />
    <property name="itemName" value="#{itemBean.name}" />
  </bean>

Full configuration file.

<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
  <bean id="itemBean" class="com.java2s.common.Item">
    <property name="name" value="itemA" />
    <property name="qty" value="10" />
  </bean>
  <bean id="myServer" class="com.java2s.common.Server">
    <property name="item" value="#{itemBean}" />
    <property name="itemName" value="#{itemBean.name}" />
  </bean>
</beans>

Download Java2s_Spring_EL_XML.zip

Spring EL in Annotation

The following example shows how to use Spring Expression Language in annotation.

First, we define a Java Bean Item and mark it with Component annotation. For its properties we use the Value annotation to assign them values

package com.java2s.common;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component("itemBean")
public class Item {
  @Value("itemA") //inject String directly
  private String name;
  @Value("10") //inject interger directly
  private int qty;
  public String getName() {
    return name;
  }
  @Override
  public String toString() {
    return "Item [name=" + name + ", qty=" + qty + "]";
  }
  public int getQty() {
    return qty;
  }
  public void setQty(int qty) {
    this.qty = qty;
  }
  public void setName(String name) {
    this.name = name;
  }
}

Then, we define a Server Java bean and also mark it with Component annotation. When defining Server's properties we use the values defined Value annotations from Item bean.

package com.java2s.common;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component("myServer")
public class Server {

  @Value("#{itemBean}")
  private Item item;

  @Value("#{itemBean.name}")
  private String itemName;

  public Item getItem() {
    return item;
  }

  public void setItem(Item item) {
    this.item = item;
  }

  public String getItemName() {
    return itemName;
  }

  public void setItemName(String itemName) {
    this.itemName = itemName;
  }

  @Override
  public String toString() {
    return "Server [item=" + item + ", itemName=" + itemName + "]";
  }

}

Finally, we have to enable auto component scanning in the xml file.

<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xmlns:context="http://www.springframework.org/schema/context"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
  http://www.springframework.org/schema/context
  http://www.springframework.org/schema/context/spring-context-3.0.xsd">

  <context:component-scan base-package="com.java2s.common" />

</beans>

Example

The following code shows how to run the code above.

package com.java2s.common;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class App {
  public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("SpringBeans.xml");
      Server obj = (Server) context.getBean("myServer");
      System.out.println(obj);
  }
}

The code above generates the following result.

Download Java2s_spring_EL_Annotation.zip

Collections in Spring Expression Language

The following code shows how to use Collections in Spring Expression Language.

First, define a Java bean with collections in it.

package com.java2s.common;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.springframework.stereotype.Component;

@Component("testBean")
public class Test {

  private Map<String, String> map;
  private List<String> list;

  public Test() {
    map = new HashMap<String, String>();
    map.put("MapA", "This is A");
    map.put("MapB", "This is B");
    map.put("MapC", "This is C");

    list = new ArrayList<String>();
    list.add("List0");
    list.add("List1");
    list.add("List2");
  }
}

Then, use the collection in the expression language.

package com.java2s.common;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component("customerBean")
public class Customer {

  @Value("#{testBean.map['MapA']}")
  private String mapA;

  @Value("#{testBean.list[0]}")
  private String list;

}

Use the same settings in the xml configuration file.

<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

  <bean id="customerBean" class="com.java2s.common.Customer">
    <property name="mapA" value="#{testBean.map['MapA']}" />
    <property name="list" value="#{testBean.list[0]}" />
  </bean>

  <bean id="testBean" class="com.java2s.common.Test" />

</beans>