Jsp&Servlet之Session对象

login.jsp 
<form action= "login.jsp" method= "post"> 
          账号：<input type= "text" name= "uname"><br> 
          密码：<input type= "password" name= "upw"><br> 
          <input type= "submit" value= "登    陆">            
        </form> 
         
        <% 
           if(request.getParameter( "uname") !=  null && request.getParameter( "upw") != null){    
            
            String name = request.getParameter( "uname"); 
            String pw = request.getParameter( "upw");            
            
             if(name.equals( "admin")&& pw.equals( "1234")){ 
             
             //若用户成功登陆，则设置flag属性值为OK 
             //则在欢迎页上，根据属性flag值的判定，可以知道用户是否登陆成功了 
             
              session.setAttribute( "flag", "OK"); 
                
               //可以利用session把用户名传递给欢迎页 
              session.setAttribute( "uname",name); 
             
             //登陆成功后，跳转至欢迎页 
              response.sendRedirect( "welcome.jsp"); 
             
            } else{            
        %> 
          <h1>登陆失败！</h1> 
        <% 
            } 
          } 
        %> 

welcome.jsp 
<%-- 欢迎页：先判定用户是否已经成功登陆（根据属性flag是否被设置） 
             
            若flag有值，说明登陆验证是成功的，则显示欢迎消息 
             
            否则，3秒钟后转回 login.jsp页 
             
     --%> 
 
<%    
           if(session.getAttribute( "flag")!=  null){ 
 %> 
          <h1>欢迎<%= (String)session.getAttribute( "uname") %>光临！</h1> 
 <% 
          } else{            
 %>         
            <h1>您还未登陆，请登陆后再访问！</h1>             
 <% 
          response.setHeader( "refresh", "3;url=login.jsp"); 
          } 
 %>