index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>$Title$</title>
  </head>
 
  <body>
  <form action="dologin.jsp" method="post" >
    用户名:<input type="text" name="username"/>
    <br>
    密码:<input type="password"  name="password"/>
    <br>
    <input type="submit" value="登录">
  </form>
  </body>
</html>

login.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>接受密码并验证</title>
</head>
<body>
<%                    
    String username = request.getParameter("username");
    String password = request.getParameter("password");
    System.out.println(username);
    String rightUsername ="";
    String rightPassword ="";
 
       
    try {
        Class.forName("com.mysql.jdbc.Driver");
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/firsttry", "root", "root");
        PreparedStatement preparedStatement = connection.prepareStatement("select * from jsp where username=?");
        preparedStatement.setString(1, "zhangsan");
        ResultSet resultSet = preparedStatement.executeQuery();
        System.out.println(resultSet);
        while (resultSet.next()) {
            rightUsername = resultSet.getString("username");
            rightPassword = resultSet.getString("userpassword");
        }
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }
 
 
        if (username.equals(rightUsername) && password.equals(rightPassword)) {
            session.setAttribute("username", username);
            response.sendRedirect("success.jsp");
        } else {
            response.sendRedirect("index.jsp");
        }
 
%>
</body>
</html>

dologin.jsp

<%@ page import="java.sql.*" %><%--
  Created by IntelliJ IDEA.
  User: Dell
  Date: 2021/4/10
  Time: 14:38
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<%
    String uname = request.getParameter("username");
    String upwd = request.getParameter("password");
    String inputVcode = request.getParameter("inputVcode").toLowerCase();
    String realInputVcode =(String) session.getAttribute("codes");

    String realUname="";
    String reaslPassword = "";

    Class.forName("com.mysql.jdbc.Driver");

    Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mysql","root","root");

    PreparedStatement preparedStatement =connection.prepareStatement("SELECT * FROM dl where uname = ?");
    preparedStatement.setString(1,uname);


    ResultSet rs = null;
    try {
        rs = preparedStatement.executeQuery();
    } catch (SQLException e) {
        e.printStackTrace();
    }
    //如果有数据，rs.next()返回true
    while(rs.next()){
       realUname = rs.getString("uname");
       reaslPassword = rs.getString("upwd");
    }

    if(uname.equals(realUname)&&upwd.equals(reaslPassword)&&inputVcode.equals(inputVcode)){
        HttpSession httpSession = request.getSession();
        httpSession.setAttribute("username",uname);
        httpSession.setAttribute("password",upwd);
        response.sendRedirect("success.jsp");
    }else {
        response.sendRedirect("login.jsp");
    }
%>
</body>
</html>

success.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<%
String username = (String) session.getAttribute("username");
%>
       恭喜您<%=username%>登录成功
</body>
</html>