Application life cycle listeners and events

 

With application life cycle listeners and events, which are now part of the Servlet API, you can notify interested listeners when servlet contexts and sessions change. For example, you can notify users when attributes change and if sessions or servlet contexts are created or destroyed.

The life cycle listeners give the application developer greater control over interactions with ServletContext and HttpSession objects. Servlet context listeners manage resources at an application level. Session listeners manage resources that are associated with a series of requests from a single client. Listeners are available for life cycle events and for attribute modification events. The listener developer creates a class that implements the javax listener interface, corresponding to the listener functionality that you want.

At application startup time, the container uses introspection to create an instance of your listener class and registers it with the appropriate event generator.

When a servlet context is created, the contextInitialized method of your listener class is invoked, which creates the database connection for the servlets in your application to use if this context is for your application. All servlet context listeners are notified of context initialization before any servlet in the Web application is initialized.

When the servlet context is destroyed, your contextDestroyed method is invoked, which releases the database connection, if this context is for your application. You must destroy all servlets before any servlet context listeners are notified of context destruction.

Notifications to session listeners precedes notifications to context listeners.

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Related Reference

Listener classes for servlet context and session changes
Example: Creating a servlet context listener with com.ibm.websphere.DBConnectionListener.java
Web applications: Resources for learning