# Listeners

Listeners are new feature in the Sun Microsystems Java™ Servlet 2.3 Specification. A listener can be used to monitor and react to events in a servlet's life-cycle by defining methods that get invoked when life-cycle events occur. Support for application level events is defined in the Java Servlet Specification 2.3.

Application event listeners are classes that implement one or more of the servlet event listener interfaces. Servlet event listeners support notification for state changes in the ServletContext and HttpSession objects, specifically:

- Servlet context listeners are used to manage resources or state held at a VM level for the application.
- HTTP session listeners are used to manage state or resources associated with a series of requests made in a Web application from the same client or user.

For more information about listeners, refer to the Sun Microsystems Java Servlet 2.3 Specification at `java.sun.com/products/servlet/download.html`.

Related concepts
Servlets
Listeners
Web application overview
Related tasks
Creating Servlets
Creating Listeners
Creating Filters