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

Example

Here’s a SetFactoryBean example, it will instantiate a HashSet at runtime.

package com.mkyong.common;
 
import java.util.Set;
 
public class Customer 
{
	private Set sets;
 
	public Set getSets() {
		return sets;
	}
 
	public void setSets(Set sets) {
		this.sets = sets;
	}
 
	@Override
	public String toString() {
		return "Customer [sets=" + sets + "]" + 
		       " Type=[" + sets.getClass() + "]";
	}
}

Spring’s bean 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-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 the util schema and <util:set> to achieve the same thing.

<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(new String[] {"Spring-Customer.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 and injected a HashSet into Customer’s sets property at runtime.

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