java web 程序---登陆验证session。提示登陆

loigin.jsp

<%@ page language="java" import="java.util.*" pageEncoding="gb2312"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>

    <title>My JSP 'login.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->

  </head>

  <body>
  <form action="check.jsp">
  账号： <input type="text" name="user"/><br/>
   密码：<input type="text" name="pass"/><br/>
   <input type="submit" value="登陆"/>
   </form>
  </body>
</html>

check.jsp

<%@ page language="java" import="java.util.*" pageEncoding="gb2312"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>

    <title>My JSP 'check.jsp' starting page</title>

	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

  </head>

  <body>
    <%
    	String name=request.getParameter("user");
    	String pass=request.getParameter("pass");
    	if(name.equals("abc")&&pass.equals("mas")){

    	session.setAttribute("name",name);
    	session.setAttribute("pass",pass);

    	%>
    <jsp:forward page="a.jsp"/>
    <%	}else{
    	out.print("你好，你的输入有误！");
    %>
    		<a href ="login.jsp">重新登陆</a>

    	<%}%>

  </body>
</html>

　　a.jsp

<%@ page language="java" import="java.util.*" pageEncoding="gb2312"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>

    <title>My JSP 'a.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->

  </head>

  <body>
    <%

        String a=(String)session.getAttribute("name");
        String b=(String)session.getAttribute("pass");
        if(a==null||b==null){%>
        <jsp:forward page="b.jsp"/>

        <%}%>

     登陆成功
  </body>
</html>

b.jsp

<%@ page language="java" import="java.util.*" pageEncoding="gb2312"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
      <title>My JSP 'b.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->

  </head>

  <body>
请先登陆
<a href="login.jsp">重新登陆</a>
  </body>
</html>