JAVA EXAMPLE PROGRAMS

JAVA EXAMPLE PROGRAMS

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Spring Bean Post Processors


BeanPostProcessor gives you a way to do some operations before creating the spring bean and immediately after creating the spring bean. This allows you to add some custom logic before and after spring bean creation. The BeanPostProcessors operate on bean (or object) instances which means that the Spring IoC container instantiates a bean instance and then BeanPostProcessor interfaces do their work.

Notice that the init and destroy methods related to bean are different from bean post processors. BeanPostProcessors are common for all beans. This example clearly shows the difference from them.

To implement bean post processor logic, we need to create a class which implements BeanPostProcessor interface and two of its methods.

package com.java2novice.beans;

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

public class MyBeanInitProcessor implements BeanPostProcessor{

	@Override
	public Object postProcessAfterInitialization(Object bean, String beanName)
			throws BeansException {
		System.out.println("before initialization: "+beanName);
		return bean;
	}

	@Override
	public Object postProcessBeforeInitialization(Object bean, String beanName)
			throws BeansException {
		System.out.println("after initialization: "+beanName);
		return bean;
	}
}

Bean class:

package com.java2novice.beans;

import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

public class NetworkManager{

	private HttpURLConnection connection;
	private String urlStr;
	
	public void setUrlStr(String urlStr){
		this.urlStr = urlStr;
	}
	
	@PostConstruct
	public void init(){
		
		System.out.println("Inside init() method...");
		URL obj;
		try {
			obj = new URL(this.urlStr);
			//initialize http connection here
			this.connection = (HttpURLConnection) obj.openConnection();
		} catch (MalformedURLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
	@PreDestroy
	public void destroy(){
		try{
			System.out.println("Inside destroy() method...");
			if(this.connection != null) {
				connection.disconnect();
			}
		} catch(Exception ex){
			
		}
	}
	
	public void readData(){
		try {
			int responseCode = this.connection.getResponseCode();
			System.out.println("Response code: "+responseCode);
			/**
			 * do your business logic here
			 */
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

Xml based configuration file, note that we registered BeanPostProcessor implementor class here:

<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
	http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
	http://www.springframework.org/schema/context
	http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <context:annotation-config />
    
    <bean id="netManager" class="com.java2novice.beans.NetworkManager">
    	<property name="urlStr" value="http://www.google.com/search?q=java2novice"/>    
    </bean>
    
    <bean class="com.java2novice.beans.MyBeanInitProcessor" />
</beans>

Spring bean demo class:

package com.java2novice.test;

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

import com.java2novice.beans.NetworkManager;

public class SpringDemo {

	public static void main(String a[]){
		String confFile = "applicationContext.xml";
		ConfigurableApplicationContext context 
							= new ClassPathXmlApplicationContext(confFile);
		NetworkManager networkMng = (NetworkManager) context.getBean("netManager");
		networkMng.readData();
		context.close();
	}
}

Output:
after initialization: netManager
Inside init() method...
before initialization: netManager
Response code: 403
Inside destroy() method...
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Knowledge Centre
doPost Vs doGet methods
doGet() method is used to get information, while doPost() method is used for posting information. doGet() requests can't send large amount of information and is limited to 240-255 characters. However, doPost()requests passes all of its data, of unlimited length. A doGet() request is appended to the request URL in a query string and this allows the exchange is visible to the client, whereas a doPost() request passes directly over the socket connection as part of its HTTP request body and the exchange are invisible to the client.
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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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