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。

CREATE DATABASE j_db;
USE j_db;
CREATE TABLE jsp_data(uname VARCHAR(10),upwd VARCHAR(10));
INSERT INTO jsp_data(uname,upwd)VALUES('张三',111);
INSERT INTO jsp_data(uname,upwd)VALUES('李四',222);
INSERT INTO jsp_data(uname,upwd)VALUES('王五',333);

　　

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<html>
  <head>
    <title>$Title$</title>
    <link rel="stylesheet" href="./layui/css/layui.css">
    <link rel="stylesheet" href="./css/adminLogin.css">
  </head>
  <body>

  <div>
    <img src="img/4.jpg" class="imgStyle">
    <div >
      <form action="get.jsp" method="POST">
        <div >
        </div>
        <div >
          <div>
            <label>用户名:</label>
          </div>
          <div>
            <i class="layui-icon layui-icon-username adminIcon"></i>
            <input id="loginUsername" class="layui-input adminInput" type="text" name="name"
                   placeholder="输入用户名">
          </div>
        </div>
        <div>
          <div>
            <label>密码:</label>
          </div>
          <div>
            <i class="layui-icon layui-icon-password adminIcon"></i>
            <input id="loginPassword" class="layui-input adminInput" type="password" name="password"
                   placeholder="输入密码">
          </div>
        </div>
        <div>
          <div>
            <label>验证码:</label>
          </div>
          <div>
            <input id="loginCard" class="layui-input cardInput" type="text" name="card" placeholder="输入验证码">
          </div>
          <div id="code_box" class="codeDiv">4j8k
          </div>
        </div>
        <div>
          <div>
            <label>没有账号？<a href="#" id="loginRegister">点击注册</a></label>
          </div>
          <div>
            <input id="loginBtn" type="submit" class="submit layui-btn layui-btn-primary"
                   value="登录"></input>
          </div>
        </div>
      </form>
    </div>
  </div>

  <script>
    var code_box = document.getElementById("code_box");

    function refreshCode() {

    
      var code = '0123456789qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM',
              char = '',
              result = '';

      for (var i = 0; i < 4; i++) {

       
        var code_index = Math.round(Math.random() * 61);
       
        var char = code[code_index];
       
        if (result.toUpperCase().indexOf(char.toUpperCase()) > -1)
                
        {
          i--;
      
          continue; 
        }
        result += char;
      }
      code_box.innerHTML = result;
    }
 
    code_box.onclick = refreshCode;
  </script>
  </body>
</html>

　　

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<%
    PreparedStatement pre = null;
    Statement sql;
    ResultSet rs;
    request.setCharacterEncoding("utf-8");
    String Name = request.getParameter("name");  //获取输入的用户名
    String Ps = request.getParameter("password");  // 密码
    Name.trim();
    Ps.trim();
    request.setCharacterEncoding("utf-8");

    Class.forName("com.mysql.cj.jdbc.Driver");
    // 建立连接
    Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/j_db?serverTimezone=GMT", "root", "135790");
    sql =conn.createStatement();
    String SQL = "select * from jsp_data where uname=? and upassword=?";
    pre=conn.prepareStatement(SQL);
    pre.setString(1,Name);
    pre.setString(2,Ps);
    rs=pre.executeQuery();
    if (rs.next()) {
        String name = rs.getString(1);
        session.setAttribute("name",name);
%><p>欢迎登陆：<%=name%></p><%
      }else{%> <p>输入错误，请重新登录</p><a href="index.jsp"><button>返回登录界面</button></a>
<%
      }
      rs.close();
    sql.close();
    conn.close();
    %>
</body>
</html>