How do I inject collections using set element in Spring?

In this example you will see how to use the <set> element to wire a collection property of a bean. We will reuse the bean that we use in the previous example How do I inject collections using list element in Spring?.

The Album bean have a songs property that have a type of java.util.List. The <set> element doesn’t have to be used with java.util.Set. It can be used to wire a java.util.List collection. It just mean the it cannot contains duplicate values in it, so the collection will only contains a unique values.

Here how we configure our Spring context:

<?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="album" class="org.kodejava.example.spring.collections.Album">
        <property name="title" value="Please Please Me"/>
        <property name="year" value="1963"/>
        <property name="songs">
            <set>
                <ref bean="song1"/>
                <ref bean="song1"/>
                <ref bean="song1"/>
            </set>
        </property>
    </bean>

</beans>

The <set> configuration can bee seen in the album bean configuration. We set the songs property. Within this property element we use the <set> element. And then using the <ref> element we add some bean into the collection.

Create the following code to run it:

package org.kodejava.example.spring.collections;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class DemoSet {
    public static void main(String[] args) {
        ApplicationContext context =
                new ClassPathXmlApplicationContext(
                        new String[] {"CollectionSet.xml"});

        Album album = (Album) context.getBean("album");
        System.out.println("Album = " + album);
    }
}

You’ll see the following output in the screen. As you can see, although we set three beans into the songs property, the Album bean only contain a single song. This is because we use the <set> element to wire the collection. It doesn’t allow duplicate values.

Album = Album{title='Please Please Me', year=1963, 
    songs=[Song{title='I Saw Her Standing There', writer='Beatles'}, null], 
    publisher={}, 
    props={}}

Wayan

Programmer, runner, recreational diver, live in the island of Bali, Indonesia. Mostly programming in Java, creating web based application with Spring Framework, Hibernate / JPA.

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