BeanPostProcessors in Spring

This is 12 of 13 parts of tutorial series

Tutorial Content:

Part-1:Introduction to spring framework
Part-2:Dependency injection(ioc) in spring
Part-3:Spring hello world example in eclipse
Part-4:Dependency injection via setter method in spring
Part-5:Dependency injection via constructor in spring
Part-6:Spring Bean scopes with examples
Part-7:Initializing collections in spring
Part-8:Beans Autowiring in spring 
Part-9:Inheritance in Spring 
Part-10:Spring ApplicationContext 
Part-11:Spring lifetime callbacks 
Part-12:BeanPostProcessors in Spring 
Part-13:Annotation based Configuration in spring 

BeanPostProcessors interface provides methods that you can implement to have your own instantiation logic.Also you can write your own logic after spring IOC finishes instantiating, configuring, and initializing a bean by plugging in one or more BeanPostProcessor implementations.

You can configure multiple BeanPostProcessors and also can decide the order in which they will run relative to each other by setting order property but foe that BeanPostProcessors  have to implement ordered interface.

Extension of BeanPostProcessor is BeanFactoryPostProcessor interface which allows direct modification of bean definitions before a bean is instantiated

An ApplicationContext will automatically register and process a bean that implements either of these interfaces, but a BeanFactory would have to have a BeanPostProcessor or BeanFactoryPostProcessor registered with it programatically.

Example:

For configuring spring in your eclipse ide please refer  hello world example

1.Country.java:

This is simple pojo class having some attributes so here country has name.

Create Country.java under package org.arpit.javapostsforlearning.Copy following content into Country.java.

package org.arpit.javapostsforlearning;

public class Country {

	String countryName ;
	
	public String getCountryName() {
		return countryName;
	}
	
	
	public void setCountryName(String countryName) {
		this.countryName = countryName;
	}

	public void init()
	{
		System.out.println("In init block of country");
	}

	public void destroy()
	{
		System.out.println("In destroy block of country");
	}
}

2.InitCapitalPostProcessor.java:

This is simple pojo class implementing BeanPostProcessor interface.

Create InitCapitalPostProcessor.java under package org.arpit.javapostsforlearning.Copy following content into InitCapitalPostProcessor.java.

package org.arpit.javapostsforlearning;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;

public class InitCapitalPostProcessor implements BeanPostProcessor{

	public Object postProcessAfterInitialization(Object bean, String beanName)
			throws BeansException {
		System.out.println("AfterInitialization : " + beanName);
	      return bean;  // you can return any other object as well
	}

	public Object postProcessBeforeInitialization(Object bean, String beanName)
			throws BeansException {
		
	      System.out.println("BeforeInitialization : " + beanName);
	      return bean;  // you can return any other object as well
	}

}

 Here we are writing very simple logic but you can write quite complex logic  in above functions.You can note that you have object of bean class here so you can change it in whatever way you want and can return same or different object.

3.BeanPostProcessorExampleMain.java

This class contains main function.Create BeanPostProcessorExampleMain.java under package org.arpit.javapostsforlearning.Copy following content into BeanPostProcessorExampleMain.java

package org.arpit.javapostsforlearning;

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

public class BeanPostProcessorExampleMain{

	public static void main(String[] args) {

		AbstractApplicationContext appContext = new ClassPathXmlApplicationContext("ApplicationContext.xml");
		Country countryObj = (Country) appContext.getBean("country");
		System.out.println("Country Name: "+countryObj.getCountryName());
		appContext.registerShutdownHook();
	}
}

Here you need to register a shutdown hook registerShutdownHook() method that is declared on the AbstractApplicationContext class. This will ensures a graceful shutdown and calls the relevant destroy methods.

4.ApplicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

	<bean id="country" class="org.arpit.javapostsforlearning.Country" init-method="init" destroy-method="destroy">
	<property name="countryName" value="India"/>
	</bean>
      <bean class="org.arpit.javapostsforlearning.InitCapitalPostProcessor"/> 
 </beans>

5.Run it

When you will run above application,you will get following as output.

BeforeInitialization : country
In init block of country
AfterInitialization : country
Country Name: India
In destroy block of country