An Event Listener is a class that implements one or more of the
event listener interfaces included with the Java Servlet API, version 1.3. The
interfaces are used for four different kinds of events that can be monitored by
an event listener:
- javax.servlet.ServletContextListener - Used to monitor lifecycle events
of a servlet context.
- javax.serlvet.ServletContextAttributeListener - Used to monitor changes
to the servlet context's attributes.
- javax.servlet.http.HttpSessionListener - Used to monitor the lifecycle
of an HTTP session.
- javax.servlet.http.HttpSessionAttributesListener - Used to monitor changes
to an HTTP session's attributes.
The event listeners are listed in the order that they are invoked. One example
of an event listener is a servlet context listener class that manages a
database connection. When the application starts, the listener class is
notified so that it can log on to the database and store the connection in the
servlet context. When the web server is shut down, or the application is removed
from the web server, the listener is notified so that it can close the database
connection.