10.9.1 Session listeners

Some listener classes are defined in the Servlet 2.4 specification to listen for state changes of a session and its attributes. This allows greater control over interactions with sessions, leading programmers to monitor creation, deletion, and modification of sessions. Programmers can perform initialization tasks when a session is created, or clean up tasks when a session is removed. It is also possible to perform some specific tasks for the attribute when an attribute is added, deleted, or modified.

The following are the Listener interfaces to monitor the events associated with the HttpSession object:

• javax.servlet.http.HttpSessionListener

  Monitor creation and deletion, including session timeout, of a session.

• javax.servlet.http.HttpSessionAttributeListener

  Monitor changes of session attributes, such as add, delete, and replace.

• javax.servlet.http.HttpSessionActivationListener

  Monitor activation and passivation of sessions. Useful to monitor if the session exists, whether in memory or not, when persistent session is used.

Listener interfaces and their methods...

Target	Event	Interface	Method
session	create	HttpSessionListener	sessionCreated()
	destroy	HttpSessionListener	sessionDestroyed()
	activate	HttpSessionActivationListener	sessionDidActivate()
	passivate	HttpSessionActivationListener	sessionWillPassivate()
attribute	add	HttpSessionAttributeListener	attributeAdded()
	remove	HttpSessionAttributeListener	attributeRemoved()
	replace	HttpSessionAttributeListener	attributeReplaced()

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