HttpSessionListener和HttpSessionAttributeListener

public interface HttpSessionListener
extends java.util.EventListener
Implementations of this interface are notified of changes to the list of active sessions in a web application. To receive notification events, the implementation class must be configured in the deployment descriptor for the web application

void sessionCreated(HttpSessionEvent se)
          Notification that a session was created.
void sessionDestroyed(HttpSessionEvent se)
          Notification that a session is about to be invalidated.


HttpSessionAttributeListener监听
HttpSession中的属性的操作。当在Session增加一个属性时，激发attributeAdded(HttpSessionBindingEvent se) 方法；当在Session删除一个属性时，激发attributeRemoved(HttpSessionBindingEvent se)方法；当在Session属性被重新设置时，激发attributeReplaced(HttpSessionBindingEvent se) 方法。