servlet监听器教程(含代码)

package cn.mldn.lxh.listener ; import java.util.* ; import javax.servlet.* ; import javax.servlet.http.* ; public class OnLineDemo implements ServletContextListener,HttpSessionListener,HttpSessionAttributeListener { // 声明一个ServletContext对象 private ServletContext application = null ; public void contextInitialized(ServletContextEvent sce) { // 容器初始化时，向application中存放一个空的容器 this.application = sce.getServletContext() ; this.application.setAttribute("alluser",new ArrayList()) ; } public void contextDestroyed(ServletContextEvent sce) {} public void sessionCreated(HttpSessionEvent se) {} public void sessionDestroyed(HttpSessionEvent se) { // 将用户名称从列表中删除 List l = (List)this.application.getAttribute("alluser") ; String value = (String)se.getSession().getAttribute("uname") ; l.remove(value) ; this.application.setAttribute("alluser",l) ; } public void attributeAdded(HttpSessionBindingEvent se) { // 如果登陆成功，则将用户名保存在列表之中 List l = (List)this.application.getAttribute("alluser") ; l.add(se.getValue()) ; this.application.setAttribute("alluser",l) ; } public void attributeRemoved(HttpSessionBindingEvent se) {} public void attributeReplaced(HttpSessionBindingEvent se) {} }; /* <listener> <listener-class>cn.mldn.lxh.listener.OnLineDemo</listener-class> </listener> */