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.
| 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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