In this example you will see how to wire map collections. For this purpose we can use the <map> element in the Spring configuration file. This element declares the java.util.Map. We will reuse the bean that we use in the previous example How do I inject collections using list element in Spring?.
The <map> element can have many <entry> element with the key and value-ref attribute.
Here is the configuration example:
<?xml version="1.0" encoding="UTF-8"?>
<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="song1" class="org.kodejava.example.spring.collections.Song">
<property name="title" value="I Saw Her Standing There" />
<property name="writer" value="Beatles" />
</bean>
<bean id="song2" class="org.kodejava.example.spring.collections.Song">
<property name="title" value="Misery" />
<property name="writer" value="Beatles" />
</bean>
<bean id="song3" class="org.kodejava.example.spring.collections.Song">
<property name="title" value="Anna (Go to Him)" />
<property name="writer" value="Beatles" />
</bean>
<bean id="publisher" class="org.kodejava.example.spring.collections.Publisher">
<property name="name" value="EMI Studios"/>
</bean>
<bean id="album" class="org.kodejava.example.spring.collections.Album">
<property name="title" value="Please Please Me"/>
<property name="year" value="1963"/>
<property name="publisher">
<map>
<entry key="publisher" value-ref="publisher"/>
</map>
</property>
</bean>
</beans>
The <map> element can have many <entry> elements. We can use the key attribute to use a string as its key. If you want the key to be a reference to other bean in the Spring context you can use the key-ref instead.
The value-ref is used to set the value to refer to another bean. If the value is a simple value such as string you can use the value attribute.
To run it create the following program:
package org.kodejava.example.spring.collections;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class DemoMap {
public static void main(String[] args) {
ApplicationContext context =
new ClassPathXmlApplicationContext(
new String[] {"CollectionMap.xml"});
Album album = (Album) context.getBean("album");
System.out.println("Album = " + album);
}
}
And here what you’ll get on the console:
Album = Album{title='Please Please Me', year=1963,
songs=[],
publisher={publisher=Publisher{name=EMI Studios}},
props={}}
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