Servlet: HttpSessionEvent and HttpSessionListener
HttpSessionEvent class gives notifications for changes to sessions within a web application. HttpSessionListener receives notifications of changes to the list of active sessions in a web application and perform some action. HttpSessionListener is used to perform some important tasks when a session is created or destroyed. For example: counting the number of active session.
Servlet: Some other Session related Listeners
| Listener | Description |
|---|
| HttpSessionActivationListener | Let's you know when a session moves from one Virtual machine to another. |
| HttpSessionBindingListener | Le's your attribute class object get notified when they are added or removed from session. |
| HttpSessionAttributeListener | Let's you know when any attribute is added, removed or replaced in a session. |
Methods of HttpSessionListener
| Methods | Description |
|---|
void sessionCreated(HttpSessionEvent e) | notification that a session was created. |
void sessionDestroyed(HttpSessioEvent e) | notification that a session was destroyed. |
Example of HttpSessionListener
In this example we will create a session listener that will count the number of active sessions in a web application.
MySessionCounter.java
import javax.servlet.http.*;
public class MySessionCounter implements HttpSessionListener {
private static int sessionCount;
public int getActiveSession()
{
return sessionCount;
}
public void sessionCreated(HttpSessionEvent e)
{
sessionCount++;
}
public void sessionDestroyed(HttpSessionEvent e)
{
sessionCount--;
}
}
web.xml
<web-app ...>
<listener>
<listener-class>MySessionCounter</listener-class>
</listener>
</web-app>
