Project Confucius: Listeners

Saturday, February 25, 2012

Listeners

Sometimes your web application needs to know about lifecycle events - such as when a new session starts, a session expires, an attribute is added to the context, etc.

You can write a Listener class and register it in web.xml.

In your /src/org/confucius folder, create a class SessionTimeoutListener.java, like this:

 package org.confucius;  
   
 import javax.servlet.http.HttpSessionEvent;  
 import javax.servlet.http.HttpSessionListener;  
   
 import org.apache.log4j.Logger;  
 import org.apache.log4j.PropertyConfigurator;  
   
 public class SessionTimeoutListener implements HttpSessionListener {  
      private Logger logger;  
        
      public SessionTimeoutListener(){  
     PropertyConfigurator.configure("log4j.properties");    
     logger = Logger.getLogger(HelloWorld.class);      
       }  
        
      public void sessionCreated(HttpSessionEvent event) {  
           logger.info("Session created.");  
      }  
   
      public void sessionDestroyed(HttpSessionEvent event) {  
           logger.info("Session destroyed.");  
      }  
   
 }

This is a Listener class - it implements the HttpSessionListener interface.
It is notified whenever a session is created and destroyed.

Note that we have used log4j to write logs - this post explains how to use log4j.

Register this class in your web.xml, like this:

 <web-app>   
      <listener>  
           <listener-class>org.confucius.SessionTimeoutListener</listener-class>  
      </listener>  
        
      <session-config>  
            <session-timeout>1</session-timeout>  
      </session-config>  
 </web-app>

That's it.
Note that we are specifying a session timeout of 1 minute.

In your /web-content/jsp folder, create a file home.jsp, like this:

 <html>  
      <body>  
           <p>Welcome to Confucius</p>  
      </body>  
 </html>

Build and deploy HelloWorld.war, then point your nrowser to:
http://localhost:8080/HelloWorld/jsp/home.jsp

This will start a new session.

If you open your HelloWorld.log file (in <tomcat_install_dir>/logs), you will see a log for when the session was created.

Saturday, February 25, 2012

Listeners

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