The session listener works on the creation of the web session and also destroys it. Here's a simple example that logs the two events:

@WebListener
public class SampleSessionListener implements HttpSessionListener {
 private static final Logger logger = getLogger(SampleSessionListener.class.getName());
   @Override
 public void sessionCreated(HttpSessionEvent se) {
      logger.info("MySessionListener.sessionCreated: " + se.getSession().getId());
   }
   @Override
 public void sessionDestroyed(HttpSessionEvent se) {
      logger.info("MySessionListener.sessionDestroyed: " + se.getSession().getId());
   }
}

Each listener must declare the javax.servlet.annotation.WebListener annotation. The session listener must implement the javax.servlet.http.HttpSessionListener interface.