web.xml中listener的作用及使用
<%
session=request.getSession(false);
if(session!=null)session.invalidate();
%>
<html>
<head><title></title></head>
<body>
<form action="isOnline.jsp" method="post">
用户名：<input type="text" name="uName"/>
<input type="submit" value="上线">
</form>
</body>
</html>
2、控制页面（只是为了说明监听器问题，所以简单了点...） isOnline.jsp
<%@page pageEncoding="gb2312" contentType="text/html; charset=gb2312" %>
<html>
<head><title></title></head>
<body>
<%
session=request.getSession();
session.setAttribute("userName",request.getParameter("uName"));
response.sendRedirect("showOnline.jsp");
%>
</body>
</html>
3、显示页面 showOnline.jsp
<%@page pageEncoding="gb2312" contentType="text/html; charset=gb2312" import="java.util.ArrayList" %>
<html>
<head><title></title></head>
<body>
<%
ArrayList showList=(ArrayList)(getServletContext().getAttribute("list"));
out.print("在线人数 "+showList.size()+"<br>");
for(int i=0;i<showList.size();i++){
out.print(showList.get(i)+"在线"+"<br>");
}
%>
<br>
<a href="Login.jsp">退出</a>
</body>
</html>
4、配置页面 <!DOCTYPE ??? "http://java.sun.com/dtd/package javax.servlet.http;import java.util.EventListener;public abstract interface HttpSessionAttributeListener extends EventListener{ public abstract void attributeAdded(HttpSessionBindingEvent paramHttpSessionBindingEvent); public abstract void attributeRemoved(HttpSessionBindingEvent paramHttpSessionBindingEvent); public abstract void attributeReplaced(HttpSessionBindingEvent paramHttpSessionBindingEvent);}
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