Handling Servlet Life-Cycle Events

<< Servlet Life Cycle | Specifying Event Listener Classes >>

Handling Servlet Life-Cycle Events

Handling Servlet Life-Cycle Events

You can monitor and react to events in a servlet's life cycle by defining listener objects whose
methods get invoked when life-cycle events occur. To use these listener objects you must define
and specify the listener class.

Defining the Listener Class

You define a listener class as an implementation of a listener interface.

Table 42

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 42

Servlet Life-Cycle Events

Object

Event

Listener Interface and Event Class

Web context (see

"Accessing the Web
Context" on page 124

)

Initialization and
destruction

javax.servlet.ServletContextListener

and

ServletContextEvent

Attribute added,
removed, or replaced

javax.servlet.ServletContextAttributeListener

and

ServletContextAttributeEvent

Session (See

"Maintaining Client
State" on page 125

)

Creation,
invalidation,
activation,
passivation, and
timeout

javax.servlet.http.HttpSessionListener

javax.servlet.http.

HttpSessionActivationListener

, and

HttpSessionEvent

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

Attribute added,
removed, or replaced

javax.servlet.ServletRequestAttributeListener

and

ServletRequestAttributeEvent

The
tut-install/javaeetutorial5/examples/web/bookstore1/src/java/com/sun/bookstore1/listeners/ContextListen
class creates and removes the database access and counter objects used in the Duke's Bookstore
application. The methods retrieve the web context object from ServletContextEvent and then
store (and remove) the objects as servlet context attributes.

Servlet Life Cycle

Chapter 4 · Java Servlet Technology

103