练习1更改

登录页

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>登录页</title>
</head>
<body>

<form action="yanzheng.jsp" method="post">

用户名：
<input type="text" name="userid" width="30"/>

密码：
<input type="password" name="mima" width="30"/>

<input type="submit" value="登录"/>

</form>
</body>
</html>

消息页

 1 <%@ page language="java" contentType="text/html; charset=UTF-8"
 2     pageEncoding="UTF-8"%>
 3     <%@ page import=java.util.*   %>
 4 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 5 <html>
 6 <head>
 7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 8 <title>消息页面</title>
 9 </head>
10 <body>
11 <%
12 
13 String strMsgID = request.getParameter("msgid");
14 
15 if(strMsgID ==null || strMsgID.trim().length()==0)
16 {
17 out.print("请正确传递信息");    
18 }
19 else
20 {
21     int msgid = Integer.parseInt(strMsgID);
22     
23     switch(msgid)
24     {
25     case 1:
26         
27         out.print("请正确输入用户名");
28         
29         break;
30         
31     case 2:
32         
33         out.print("请正确输入密码");
34         
35         break;
36         
37     case 3:
38         
39         out.print("密码输入错误");
40         
41         break;
42         
43     case 4:
44         
45         out.print("该用户不存在");
46         
47         break;
48     }
49 }
50 
51 response.setHeader("refresh", "3;URL=Login.jsp");
52 %>
53 </body>
54 </html>

验证页

 1 <%@ page language="java" contentType="text/html; charset=UTF-8"
 2     pageEncoding="UTF-8"%>
 3 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 4 <html>
 5 <head>
 6 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 7 <title>验证页</title>
 8 </head>
 9 <body>
10 <%
11 
12 String strUserid = request.getParameter("userid");
13 
14 String strPW = request.getParameter("mima");
15 
16 if(strUserid==null||strUserid.trim().length()==0)
17 {    
18     response.sendRedirect("message.jsp?msgid=1");
19 }
20 else if(strPW==null||strPW.trim().length()==0)
21 {
22     response.sendRedirect("message.jsp?msgid=2");
23 }
24 else
25 {
26 //查找用户信息
27 String strUID="zhangsan";
28 String strP ="123456";
29 
30     if(strUserid.equals(strUID))//找到
31     {
32         if(strPW.equals(strP))
33         {
34             out.print("登录成功");
35         }
36         else
37         {
38             response.sendRedirect("message.jsp?msgid=3");
39         }
40     }
41     else
42     {
43         response.sendRedirect("message.jsp?msgid=4");
44     }
45 }
46 %>
47 </body>
48 </html>

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原文地址：https://www.cnblogs.com/zxw0004/p/4999235.html