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Spring bean init and destroy methods using annotations @PostConstruct and @PreDestroy


In the previous example you have seen calling spring bean initialization and destroy methods using xml bean configurations. This page shows how to configure spring bean initialization and destroy method calls using java annotations @PostConstruct and @PreDestroy. These annotations are not belong to spring API, these are part of J2ee library common-annotations.jar file.

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, you must include context:annotation-config tag.

<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>
</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:
Inside init() method...
Response code: 403
Inside destroy() method...
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Transient and Volatile Modifiers
Transient: The transient modifier applies to variables only and it is not stored as part of its object's Persistent state. Transient variables are not serialized.

Volatile: Volatile modifier applies to variables only and it tells the compiler that the variable modified by volatile can be changed unexpectedly by other parts of the program.
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