Developing Event Listeners 

Use

You can develop event listeners and have them registered to listen to various life-cycle events of your Web applications. In this way, you can keep track of events such as application context initialization or destruction, session creation, and so on, and can react accordingly to them.

Procedure

You have to perform two basic tasks so that your event listener is ready to handle events. These are:

...

       1.      Develop an event listener class that implements the appropriate listener interface. Java Servlet 2.3 API defines the following listener interfaces and type of events:

Application Context and Session Events

Scope of Event	Event	Event Type	Event Interface
ServletContext	Initialization or destruction of a servlet context.	ServletContextEvent	ServletContextListener
ServletContext	Add, replace or remove context attribute(s).	ServletContextAttributeEvent	ServletContextAttributeListener
Session	Create, invalidate, passivate or activate a session.	HttpSessionEvent, HttpSessionActivationListener	HttpSessionListener
Session	Add, replace or remove session attribute(s).	HttpSessionBindingEvent	HttpSessionAttributeListener

       2.      You must declare the listener class in the deployment descriptor of your Web application.