servlet session listener

HttpSessionListener-创建与销毁

//@WebListener servlet3.0支持注解public class HttpSessionListenerDemo implements HttpSessionListener{    @Override    public void sessionCreated(HttpSessionEvent httpSessionEvent) {        HttpSession session = httpSessionEvent.getSession();        ServletContext servletContext = session.getServletContext();        // undo    }    @Override    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {        // undo    }}

HttpSessionActivationListener-顿化与激活

//@WebListener servlet3.0支持注解public class HttpSessionActivationListenerDemo implements HttpSessionActivationListener {    @Override    public void sessionWillPassivate(HttpSessionEvent httpSessionEvent) {    }    @Override    public void sessionDidActivate(HttpSessionEvent httpSessionEvent) {    }}

HttpSessionAttributeListener-属性值变化

//@WebListener servlet3.0支持注解public class HttpSessionAttributeListenerDemo implements HttpSessionAttributeListener {    @Override    public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {    }    @Override    public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {    }    @Override    public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {    }}

HttpSessionBindingListener-属性值删除或增加

//@WebListener servlet3.0支持注解public class HttpSessionBindingListenerDemo implements HttpSessionBindingListener {    @Override    public void valueBound(HttpSessionBindingEvent httpSessionBindingEvent) {    }    @Override    public void valueUnbound(HttpSessionBindingEvent httpSessionBindingEvent) {    }}

设计架构
监听器的设计模式是观察者模式。
事件源：HttpSession
事件：EventObject的子类，如：HttpSessionEvent和HttpSessionBindingEvent
事件监听器：EventListener的子类。

被观察者是servlet容器。观察者则是我们写的listener.通常在自已实现的listener中都会引入实际的观察者，来处理事件。

说明：web.xml的加载顺序是：【Context-Param】->【Listener】->【Filter】->【Servlet】，而同个类型之间的实际程序调用的时候的顺序是根据对应的Mapping的顺序进行调用。