Dinesh on Java

In this article Custom bean scope we will explore how to create custom scope of bean in the spring example. There are two main scopes of bean in spring singleton and prototype but spring allow us to create custom bean scope too through the interface Scope in the spring Example. As of Spring 2.0, we can define custom spring bean scope as well as modify existing spring bean scopes (except singleton and prototype scopes). So let’s see how to create custom spring bean scope with example.

Create Custom Bean Scope Class

Let’s have a look into below class MyThreadScope.java

/**
 * 
 */
package com.doj.app.scope;

import java.util.HashMap;
import java.util.Map;

import org.springframework.beans.factory.ObjectFactory;
import org.springframework.beans.factory.config.Scope;

/**
 * @author Dinesh.Rajput
 *
 */
public class MyThreadScope implements Scope {
 
 private final ThreadLocal<Object> myThreadScope = new ThreadLocal<Object>() {
  protected Map<String, Object> initialValue() {
   System.out.println("initialize ThreadLocal");
   return new HashMap<String, Object>();
  }
 };
  
 @SuppressWarnings("unchecked")
 @Override
 public Object get(String name, ObjectFactory<?> objectFactory) {
  Map<String, Object> scope = (Map<String, Object>) myThreadScope.get();
  System.out.println("getting object from scope.");
  Object object = scope.get(name);
  if(object == null) {
   object = objectFactory.getObject();
   scope.put(name, object);
  }
  return object;
 }

 @Override
 public String getConversationId() {
  return null;
 }

 @Override
 public void registerDestructionCallback(String name, Runnable callback) {

 }

 @Override
 public Object remove(String name) {
  System.out.println("removing object from scope.");
  @SuppressWarnings("unchecked")
  Map<String, Object> scope = (Map<String, Object>) myThreadScope.get();
  return scope.remove(name);
 }

 @Override
 public Object resolveContextualObject(String name) {
  return null;
 }

}

As above class for custom scope MyThreadScope, we have implemented org.springframework.beans.factory.config.Scope interface to create a own custom scope in the spring container. This interface contain five methods. But following two mandatory methods have to override to create custom spring bean scope.

• get() method – this method return the bean from the given scope.
• remove() method – this method remove an object from the scope

Register Created Custom Bean Scope

After creating the custom bean scope, we have to register it with the spring container. So there are two way to register it. Either by it programmatic registration or we can do it via using XML based configuration. Let’s have a look into both configuration as below:

Java Based Configuration:

ConfigurableApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
Scope scope = new MyThreadScope();
applicationContext.getBeanFactory().registerScope("myThreadScope", scope);

XML Based Configuration

<?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 class="org.springframework.beans.factory.config.CustomScopeConfigurer">
  <property name="scopes">
   <map>
               <entry key="myThreadScope">
                   <bean class="com.doj.app.scope.MyThreadScope"/>
               </entry>
           </map>
  </property>
 </bean>
 
 <bean id="myBean" class="com.doj.app.bean.MyBean" scope="myThreadScope"> 
  <property name="name" value="Dinesh"></property>
 </bean>
</beans>

Using the custom scope

In XML

<bean id="myBean" class="com.doj.app.bean.MyBean" scope="myThreadScope"> 
   <property name="name" value="Dinesh"></property>
</bean>

In Java

@Bean
@Scope("myThreadScope")
MyBean myBean(){
   return new MyBean();
}

Test Class for Custom Scope Example

Main.java

/**
 * 
 */
package com.doj.app.test;

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

import com.doj.app.bean.MyBean;

/**
 * @author Dinesh.Rajput
 *
 */
public class Main {
 /**
  * @param args
  */
 public static void main(String[] args) {
  ConfigurableApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
  MyBean myBean = applicationContext.getBean(MyBean.class);
  System.out.println(myBean.getName());
  System.out.println("All registered Scopes are : ");
  for(String scope : applicationContext.getBeanFactory().getRegisteredScopeNames()){
   System.out.println(scope);
  }
  applicationContext.close();
 }

}

Output on Console:

Custom Bean Scope Example with Source Code

Download this example from Github.