Spring tutorial - Spring BeanPostProcessor

We have already seen in Spring Tutorial - Bean Life Cycle in Spring, that how we can call initialization and destroy methods when the bean is created and destroyed and also how we can use @PostConstruct and @Predestroy annotations to define the init as well as destroy method.

With the end of this article we will be able to learn:

        1.     What is Spring BeanPostProcessor?

        2.     How Spring BeanPostProcessor works?

        3.     How to use Spring BeanPostProcessor?

        4.     How to register Spring BeanPostProcessor with BeanFactory?

What is Spring BeanPostProcessor?

Spring BeanPostProcessor is an interface which provides the callback method which can be implemented to do initialization work or any process that is needed to be done after the bean is instantiated, configured and initialized by the spring container.

Multiple spring BeanPostProcessor interfaces can be configured, and their order can also be decided.

How Spring BeanPostProcessor works?

The spring BeanPostProcessor interface works on bean instance, that is, the spring IoC container instantiates the bean instance, after that spring BeanPostProcessor interface method, does its work.

The ApplicationContext itself detects the beans that have implemented spring BeanPostProcessor interface and register these beans as PostProcessor and upon bean creation, they are called.

How to use Spring BeanPostProcessor? Example of Spring BeanPostProcessor

This example shows how to use Spring BeanPostProcessor in the context of ApplicationContext.

To achieve this, we will create four files HelloWorld.java, InitHelloWorld.java, MainApp.java and Beans.xml

HelloWorld.java

	package com.java8bySourabhrai;
	public class HelloWorld{
	private String message;
	public void setMessage(String message){
	this.message = message;
	}
	public void getMessage(){
	System.out.println("Your Message : " + message);
	}
	public void init(){
	System.out.println("Bean is getting initialized");
	}
	public void destroy(){
	System.out.println("Bean is getting destroyed");
	}
	}

view raw HelloWorld hosted with ❤ by GitHub

InitHelloWorld.java

	package com.java8bySourabhrai;
	import org.springframework.beans.factory.config.BeanPostProcessor;
	import org.springframework.beans.BeanException;
	public class InitHelloWorld implements BeansPostProcessor{
	public Object postProcessorBeforeInitialization(Object bean, String beanName) throws BeansException{
	System.out.println("BeforInitialization : " + beanName);
	return bean;
	}
	public Object postProcessorAfterInitialization(Object bean, String beanName) throws BeansException{
	System.out.println("AfterInitialization : " + beanName);
	return bean;
	}
	}

view raw InitHelloWorld hosted with ❤ by GitHub

MainApp.java

	package com.java8bysourabhrai;
	import org.springframework.context.ApplicationContext;
	import org.springframework.context.support.ClassPathXmlApplicationContext;
	public class MainApp{
	public static void main(String args[]){
	AbstractApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");
	HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
	obj.getMessage();
	context.registerShutdownHook();
	}
	}

view raw LifeCycleMainApp.java hosted with ❤ by GitHub

Beans.xml

	<? xml version ="1.0" encoding = "UTF-8"?>
	<beans xmlns = "http://www.springspringframework.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-3.0.xsd">
	<bean id = "helloWorld" class = "com.java8bysourabhrai.HelloWorld" init-method="init" destroy-method="destroy">
	property name = "message" value = "Hello world" />
	</bean>
	<bean class = "com.java8bysourabhrai.InitHelloWorld" />
	</beans>

view raw Beans.xml hosted with ❤ by GitHub

Once all the files are created, compile and run the application. Will give the below output.

Output

BeforeInitialization: Hello World

 Bean is getting initialized

AfterInitialization: Hello World

Your Message: Hello World

Bean is getting destroyed

 

That’s all with this topic, I hope I have covered all the required information.

The next chapter in this Spring tutorial series will be Spring – Annotation Based Configuration in Spring framework.