登陆：
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<%
request.getSession().setAttribute("user","wangfeng");
%>
用户已经登录退出：
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<%
request.getSession().removeAttribute("user");
%>
用户已经退出登录