Servlets - SPLessons

Servlet Context Listener

Chapter 25

SPLessons 5 Steps, 3 Clicks
5 Steps - 3 Clicks

Servlet Context Listener

Servlet Context Listener

shape Description

Servlet Context Listener, Modifying the condition of a particular instance is known as an event. Servlet API(Application Program interface)2.4 onwards  the event handling was introduced. Request , Session , and ServletContext objects are handled through Servlet Listeners. Event handling on request is used to keep track of the creation and destroy the request object and can be used to calculate the request processing time of each request. Following are the different methods and classes.

Classes and Methods

shape Description

On request object

On request attribute

On ServletContext object

On ServletContextAttribute

On HttpSession object


shape Example

MyAppServletContextListener.java

package servletlisteners;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class MyAppServletContextListener 
               implements ServletContextListener{
	
	@Override
	public void contextDestroyed(ServletContextEvent arg0) {
		System.out.println("ServletContextListener destroyed");
	}

        //Run this before web application is started
	@Override
	public void contextInitialized(ServletContextEvent arg0) {
		System.out.println("ServletContextListener started");	
	}
}

contextDestroyed Notification that the servlet context is about to be shut down. contextInitialized Notification that the web application initialization process is starting.
Web.xml

<web-app >
   <listener>
	<listener-class>
             servletlisteners.MyAppServletContextListener 
        </listener-class>
   </listener>
</web-app>

Output
When compile the program output will be as follows in the console.

Summary

shape Key Points

  • Servlet Context Listener – While working with events tag should be added in web.xml
  • Servlet Context Listener – The initialized and destroy methods should be called.
  • Servlet Context Listener – Through WAR file source code file needs to be deploy in Tomcat.