Example of Custom Scope in Spring

By Arvind Rai, April 16, 2013

In spring there are scopes like singleton, prototype etc. According to the requirement, spring allows to create custom scope. To understand we will create a Thread scope. Thread scope means a bean creation and destruction will be limited to a thread life cycle. We will understand it step by step.

Create Custom Scope Class

Below class is the custom thread scope. Scope is the interface and every custom scope class implements this interface and implements the methods.

CustomThreadScope.java

package com.concretepage;
import java.util.HashMap;
import java.util.Map;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.beans.factory.config.Scope;
public class CustomThreadScope implements Scope {
	CustomThreadLocal customThreadLocal = new CustomThreadLocal();
	@SuppressWarnings("rawtypes")
	@Override
	public Object get(String str, ObjectFactory objectFactory) {
		System.out.println("getting object from scope.");
    	@SuppressWarnings("unchecked")
		Map<String, Object> scope = (Map<String, Object>) customThreadLocal.get();
		Object object = scope.get(str);
		if (object == null) {
			object = objectFactory.getObject();
			scope.put(str, object);
		}
		return object;
	}
	@Override
	public String getConversationId() {
		return null;
	}
	@Override
	public void registerDestructionCallback(String arg0, Runnable arg1) {
	}
	@Override
	public Object remove(String str) {
		Map<String, Object> scope = (Map<String, Object>) customThreadLocal.get();
		return scope.remove(str);
	}
	@Override
	public Object resolveContextualObject(String arg0) {
		return null;
	}
	class CustomThreadLocal extends ThreadLocal {
		protected Map<String, Object> initialValue() {
			System.out.println("initialize ThreadLocal");
			return new HashMap<String, Object>();
		}
	}
}

Register Custom Scope

We need to register our custom scope class with spring container. We can do it in java class as well as in application XML.

app-conf.xml

<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-3.0.xsd
    http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.0.xsd">
     
     <bean class="org.springframework.beans.factory.config.CustomScopeConfigurer">
      <property name="scopes">
          <map>
              <entry key="customThread">
                  <bean class="com.concretepage.CustomThreadScope"/>
              </entry>
          </map>
      </property>
    </bean>
     
    <bean id="testA" class="com.concretepage.A"  scope="customThread" />
</beans>

SpringTest.java

package com.concretepage;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class SpringTest {
	public static void main(String[] args) {
		ApplicationContext context = new ClassPathXmlApplicationContext("app-conf.xml");
		context.getBean("testA");
	}
}

Output

getting object from scope.
initialize ThreadLocal
Bean A is initialized

Note: we can register bean in java class also. Look into the below code snippet.

 ConfigurableBeanFactory beanFactory=  new DefaultListableBeanFactory();
 Scope threadScope= new CustomThreadScope();
 beanFactory.registerScope("customThread", threadScope);

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