1.安装MySQL数据库，建立用户表 uid uname upwd 并插入3条数据

2.制作jsp登录页面 login.jsp 提交到dologin.jsp，使用jdbc连数据库，判断输入的用户名密码是否存在

3.如果存在，把用户名保存在SESSION中，跳转到welcome.jsp，welcome.jsp中读取session中的用户名，显示欢迎你xxx

4.若不存在，跳到登录页面。

login.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>


<!DOCTYPE HTML >
<html>
  <head>
   
    
    <title>登录界面</title>
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->
    <style type="text/css"> 
    .contentArea{width:450px;position:absolute;top:80px;left:250px;height:500px;} 
    </style> 
  </head>
  
  <body  style="background:url(images/3.jpg)">
  <div class="contentArea">
  <p style="font-family:黑体；font-size:56；color：yellow"></p>
  登录<br/><br/><br/>
   <form action="db.jsp"  method="post" >
   ID：<input type="text" name="uid"><br/><br/>
   密码：<input type="password" name="upwd"><br/>  <br/>
    验证码：<img src="number.jsp"/>
          <input type="text" name="code"/>
          <br/><br/>
   <input type="submit" value="登录"><br/><br/><br/><br/>
   </form>
   
   </div>
  </body >
</html>

dologin.jsp

<%@ page contentType="image/jpeg" language="java" import="java.util.*,java.awt.*,java.awt.image.*,javax.imageio.*" pageEncoding="utf-8"%>

<%
    //获取登录的用户名
    String name = request.getParameter("uname");
    //获取登录密码
    String pwd = request.getParameter("upwd");
    //判断

    if (name.equals("zs") && pwd.equals("123"))//判断字符串是否相等不是等号是eqyals
        //转发到ok页面
        request.getRequestDispatcher("ok.jsp").forward(request,response);
    else
        //转发到no页面 
        request.getRequestDispatcher("login.jsp").forward(request,response);
%>

ok.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'index.jsp' starting page</title>

    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->
    <style type="text/css"> 
    .contentArea{width:450px;position:absolute;top:150px;left:250px;height:500px;} 
    </style> 
  </head>
  
  <body  style="background:url(images/3.jpg)">
  <div class="contentArea">
  <h1 style="color: red">登录成功</h1>
   </div>
   
  </body>
</html>

no.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'index.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">
    -->
    <style type="text/css"> 
    .contentArea{width:450px;position:absolute;top:150px;left:250px;height:500px;} 
    </style> 
  </head>
  
  <body  style="background:url(images/3.jpg)">
   <div class="contentArea">
  <h1 style="color: red" >登录失败</h1>
  <h2>点击重新<a href="login.jsp">登录</a></h2>
  
   </div>
   
  </body>
</html>

db.jsp

<%@page import="java.nio.channels.SeekableByteChannel"%>
<%@ page language="java" contentType="text/html" pageEncoding="UTF-8"%>
<%@ page import="java.sql.*"%>
<html>
<head>
<title>www.school.com</title>
</head>
<body>
    <%!public static final String DBDRIVER = "com.mysql.jdbc.Driver";
    public static final String DBURL = "jdbc:mysql://localhost:3306/jspwork";
    public static final String DBUSER = "root";
    public static final String DBPASS = "root";%>
    <%
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        boolean flag = false;
        String name = null;
    %>
    <%
        try {
            Class.forName(DBDRIVER);
            conn = DriverManager.getConnection(DBURL, DBUSER, DBPASS);
            String sql = "SELECT uname FROM num_one WHERE uid=? AND upwd=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, request.getParameter("uid"));
            pstmt.setString(2, request.getParameter("upwd"));
         
            rs = pstmt.executeQuery();
            if (rs.next()) {
                name = rs.getString(1);
                flag = true;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (rs != null)
                    rs.close();
                if (pstmt != null)
                    pstmt.close();
                if (conn != null)
                    conn.close();
                if (flag) {
                 request.getSession().setAttribute("uname",name);
                 request.getRequestDispatcher("welcome.jsp").forward(request,response);
                 
                   // request.getRequestDispatcher("ok.jsp").forward(request, response);
                } else {
                    response.sendRedirect("no.jsp");
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    %>
 
</body>
</html>