Defining the Listener Class (The Java EE 6 Tutorial, Volume I)

The Java EE 6 Tutorial, Volume I

Defining the Listener Class

You define a listener class as an implementation of a listener interface. Table 10–1 lists the events that can be monitored and the corresponding interface that must be implemented. When a listener method is invoked, it is passed an event that contains information appropriate to the event. For example, the methods in the HttpSessionListener interface are passed an HttpSessionEvent, which contains an HttpSession.

Table 10–1 Servlet Life-Cycle Events


Object	Event	Listener Interface and Event Class
Web context (see Accessing the Web Context)	Initialization and destruction	`javax.servlet.ServletContextListener` and `ServletContextEvent`
Web context (see Accessing the Web Context)	Attribute added, removed, or replaced	`javax.servlet.ServletContextAttributeListener` and `ServletContextAttributeEvent`
Session (See Maintaining Client State)	Creation, invalidation, activation, passivation, and timeout	`javax.servlet.http.HttpSessionListener`, `javax.servlet.http.HttpSessionActivationListener`, and `HttpSessionEvent`
Session (See Maintaining Client State)	Attribute added, removed, or replaced	`javax.servlet.http.HttpSessionAttributeListener` and `HttpSessionBindingEvent`
Request	A servlet request has started being processed by web components	`javax.servlet.ServletRequestListener` and `ServletRequestEvent`
Request	Attribute added, removed, or replaced	`javax.servlet.ServletRequestAttributeListener` and `ServletRequestAttributeEvent`