Event Listening

A servlet can be designated as an event listener. This enables the servlet to be notified when some external event or change has occurred.

There are a number of listener interfaces that you can implement in your servlet. All the listener interfaces extend java.util.EventListener.

Table 12.6 provides a list of the listener interfaces.

Table 12.6. Servlet Event Listener Interfaces
Listener Interface Notification
HttpSessionActivationListener When a session is activated or passivated
HttpSessionAttributeListener When a session attribute is added, removed, or replaced
HttpSessionListener When a session is created or destroyed
ServletContextAttributeListener When a servlet context attribute is added, removed, or replaced
ServletContextListener ...

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