Spring SetFactoryBean example

The ‘SetFactoryBean‘ class provides developer a way to create a concrete Set collection (HashSet and TreeSet) in Spring’s bean configuration file.

package com.mkyong.common;
import java.util.Set;
public class Customer { 
    private Set sets; 
    //...
}

Spring’s bean configuration file.

<?xml version="1.0"?>
<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-2.5.xsd">
    <bean id="CustomerBean" class="com.mkyong.common.Customer">
        <property name="sets">
            <bean class="org.springframework.beans.factory.config.SetFactoryBean">
                <property name="targetSetClass">
                    <value>java.util.HashSet</value>
                </property>
                <property name="sourceSet">
                    <list>
                        <value>1</value>
                        <value>2</value>
                        <value>3</value>
                    </list>
                </property>
            </bean>
        </property>
    </bean>
</beans>

Alternatively, you also can use util schema and <util:set> to achieve the same thing.

<?xml version="1.0"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.5.xsd">
    <bean id="CustomerBean" class="com.mkyong.common.Customer">
        <property name="sets">
            <util:set set-class="java.util.HashSet">
                <value>1</value>
                <value>2</value>
                <value>3</value>
            </util:set>
        </property>
    </bean>
</beans>

Remember to include the util schema, else you will hit the following error

Caused by: org.xml.sax.SAXParseException: The prefix "util" for element "util:set" is not bound.

Run it…

package com.mkyong.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"); 
        Customer cust = (Customer)context.getBean("CustomerBean"); 
        System.out.println(cust); 
    }
}

Ouput

Customer [sets=[3, 2, 1]] Type=[class java.util.HashSet]

You have instantiated HashSet and and injected it into Customer’s sets property at runtime.