Example of Collection Merging in Spring
April 10, 2013
In spring, java collections can be injected in bean using application xml. According to the need, we can merge collection data while creating bean. There will be a parent and child bean. Child will inherit the parent data. It is done by the attribute merge="true". This attribute is available in all collection tags like <list/>, <set/>, <map/> and <props/> . The child bean will use parent attribute to inherit parent bean data. The child bean collection tag will use merge="true" attribute to inherit parent collection elements. When we access child bean, we will get elements of child as well as parent bean collection. This is collection merging of beans in spring. To understand about spring collection injection, find the link. On this page we will provide example for spring collection merging.
Collection Merging using merge="true" using XML
spring-config.xml
<?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.xsd">
<bean id="parentCollection" class="com.concretepage.bean.MyCollection">
<property name="mySet">
<set>
<value>AAAA</value>
<value>BBBB</value>
</set>
</property>
</bean>
<bean id="childCollection" parent="parentCollection">
<property name="mySet">
<set merge="true">
<value>CCCC</value>
<value>DDDD</value>
</set>
</property>
</bean>
</beans>
Create Bean
MyCollection.java
package com.concretepage.bean;
import java.util.Set;
public class MyCollection {
private Set<String> mySet;
public Set<String> getMySet() {
return mySet;
}
public void setMySet(Set<String> mySet) {
this.mySet = mySet;
}
}
Run Application
SpringDemo.java
package com.concretepage;
import java.util.Iterator;
import java.util.Set;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.concretepage.bean.MyCollection;
public class SpringDemo {
public static void main(String[] args) {
AbstractApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
MyCollection myCollection=(MyCollection)context.getBean("parentCollection");
//access parent collection
System.out.println("---Elements in parent bean---");
Set<String> parentSet=myCollection.getMySet();
Iterator<String> itrP= parentSet.iterator();
while(itrP.hasNext()){
System.out.println(itrP.next());
}
MyCollection concreteChild=(MyCollection)context.getBean("childCollection");
//access child collection
System.out.println("---Elements in child bean---");
Set<String> setC=concreteChild.getMySet();
Iterator<String> itrC= setC.iterator();
while(itrC.hasNext()){
System.out.println(itrC.next());
}
context.close();
}
}
Output
Find the output.---Elements in parent bean--- AAAA BBBB ---Elements in child bean--- AAAA BBBB CCCC DDDD
