下面给你一套**「JSP + Servlet + MySQL 登录注册系统【完整 CRUD（增删改查）】实现代码」，这是课程设计 / 实训 / 毕设小项目级别**，能直接跑、能截图、能答辩的那种。

技术栈：
JSP + Servlet + JDBC + MySQL + Session（MVC 思想）

一、系统功能总览（老师最关心）

✔ 用户注册（Create）
✔ 用户登录
✔ 用户列表查询（Read）
✔ 修改用户信息（Update）
✔ 删除用户（Delete）
✔ Session 登录控制
✔ 数据库存储

二、项目结构（标准 MVC）

jsp-crud/
│
├── src/
│   ├── entity/
│   │   └── User.java
│   ├── util/
│   │   └── DBUtil.java
│   ├── dao/
│   │   └── UserDao.java
│   ├── servlet/
│   │   ├── LoginServlet.java
│   │   ├── RegisterServlet.java
│   │   ├── UserListServlet.java
│   │   ├── UserEditServlet.java
│   │   └── UserDeleteServlet.java
│
├── WebContent/
│   ├── login.jsp
│   ├── register.jsp
│   ├── userList.jsp
│   ├── userEdit.jsp
│   └── success.jsp
│
└── web.xml

三、数据库设计（MySQL）

CREATE DATABASE jsp_crud DEFAULT CHARSET utf8;

USE jsp_crud;

CREATE TABLE user (
    id INT PRIMARY KEY AUTO_INCREMENT,
    username VARCHAR(50) UNIQUE NOT NULL,
    password VARCHAR(50) NOT NULL
);

四、数据库工具类（DBUtil）

package util;

import java.sql.*;

public class DBUtil {
    private static final String URL =
        "jdbc:mysql://localhost:3306/jsp_crud?useUnicode=true&characterEncoding=utf8";
    private static final String USER = "root";
    private static final String PASSWORD = "123456";

    static {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(URL, USER, PASSWORD);
    }
}

五、实体类（User.java）

package entity;

public class User {
    private int id;
    private String username;
    private String password;

    public User() {}

    public User(int id, String username, String password) {
        this.id = id;
        this.username = username;
        this.password = password;
    }

    // getter / setter
}

六、DAO 层（核心 CRUD）

package dao;

import entity.User;
import util.DBUtil;

import java.sql.*;
import java.util.*;

public class UserDao {

    // 注册（增）
    public void addUser(User user) throws Exception {
        String sql = "INSERT INTO user(username,password) VALUES(?,?)";
        try (Connection c = DBUtil.getConnection();
             PreparedStatement ps = c.prepareStatement(sql)) {
            ps.setString(1, user.getUsername());
            ps.setString(2, user.getPassword());
            ps.executeUpdate();
        }
    }

    // 登录（查）
    public User login(String username, String password) throws Exception {
        String sql = "SELECT * FROM user WHERE username=? AND password=?";
        try (Connection c = DBUtil.getConnection();
             PreparedStatement ps = c.prepareStatement(sql)) {
            ps.setString(1, username);
            ps.setString(2, password);
            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                return new User(
                    rs.getInt("id"),
                    rs.getString("username"),
                    rs.getString("password")
                );
            }
        }
        return null;
    }

    // 查询全部（查）
    public List<User> findAll() throws Exception {
        List<User> list = new ArrayList<>();
        String sql = "SELECT * FROM user";
        try (Connection c = DBUtil.getConnection();
             Statement s = c.createStatement();
             ResultSet rs = s.executeQuery(sql)) {
            while (rs.next()) {
                list.add(new User(
                    rs.getInt("id"),
                    rs.getString("username"),
                    rs.getString("password")
                ));
            }
        }
        return list;
    }

    // 根据 ID 查询
    public User findById(int id) throws Exception {
        String sql = "SELECT * FROM user WHERE id=?";
        try (Connection c = DBUtil.getConnection();
             PreparedStatement ps = c.prepareStatement(sql)) {
            ps.setInt(1, id);
            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                return new User(
                    rs.getInt("id"),
                    rs.getString("username"),
                    rs.getString("password")
                );
            }
        }
        return null;
    }

    // 修改（改）
    public void update(User user) throws Exception {
        String sql = "UPDATE user SET username=?,password=? WHERE id=?";
        try (Connection c = DBUtil.getConnection();
             PreparedStatement ps = c.prepareStatement(sql)) {
            ps.setString(1, user.getUsername());
            ps.setString(2, user.getPassword());
            ps.setInt(3, user.getId());
            ps.executeUpdate();
        }
    }

    // 删除（删）
    public void delete(int id) throws Exception {
        String sql = "DELETE FROM user WHERE id=?";
        try (Connection c = DBUtil.getConnection();
             PreparedStatement ps = c.prepareStatement(sql)) {
            ps.setInt(1, id);
            ps.executeUpdate();
        }
    }
}

七、Servlet 层（控制器）

1️⃣ 注册

@WebServlet("/RegisterServlet")
public class RegisterServlet extends HttpServlet {
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws IOException {
        try {
            UserDao dao = new UserDao();
            User user = new User();
            user.setUsername(req.getParameter("username"));
            user.setPassword(req.getParameter("password"));
            dao.addUser(user);
            resp.sendRedirect("login.jsp");
        } catch (Exception e) {
            resp.getWriter().write("注册失败");
        }
    }
}

2️⃣ 登录

@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws IOException {
        try {
            UserDao dao = new UserDao();
            User user = dao.login(
                req.getParameter("username"),
                req.getParameter("password")
            );
            if (user != null) {
                req.getSession().setAttribute("user", user);
                resp.sendRedirect("UserListServlet");
            } else {
                resp.getWriter().write("登录失败");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

3️⃣ 用户列表（查）

@WebServlet("/UserListServlet")
public class UserListServlet extends HttpServlet {
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws IOException, ServletException {
        try {
            UserDao dao = new UserDao();
            req.setAttribute("list", dao.findAll());
            req.getRequestDispatcher("userList.jsp").forward(req, resp);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

4️⃣ 删除

@WebServlet("/UserDeleteServlet")
public class UserDeleteServlet extends HttpServlet {
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws IOException {
        try {
            new UserDao().delete(
                Integer.parseInt(req.getParameter("id"))
            );
            resp.sendRedirect("UserListServlet");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

5️⃣ 修改（查 + 改）

@WebServlet("/UserEditServlet")
public class UserEditServlet extends HttpServlet {

    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        try {
            User user = new UserDao()
                .findById(Integer.parseInt(req.getParameter("id")));
            req.setAttribute("user", user);
            req.getRequestDispatcher("userEdit.jsp").forward(req, resp);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws IOException {
        try {
            User user = new User(
                Integer.parseInt(req.getParameter("id")),
                req.getParameter("username"),
                req.getParameter("password")
            );
            new UserDao().update(user);
            resp.sendRedirect("UserListServlet");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

八、JSP 页面

登录（login.jsp）

<form action="LoginServlet" method="post">
用户名：<input name="username"><br>
密码：<input type="password" name="password"><br>
<button>登录</button>
</form>
<a href="register.jsp">注册</a>

注册（register.jsp）

<form action="RegisterServlet" method="post">
用户名：<input name="username"><br>
密码：<input type="password" name="password"><br>
<button>注册</button>
</form>

用户列表（userList.jsp）

<%@ page import="java.util.*,entity.User" %>
<table border="1">
<tr><th>ID</th><th>用户名</th><th>操作</th></tr>
<%
for(User u : (List<User>)request.getAttribute("list")){
%>
<tr>
<td><%=u.getId()%></td>
<td><%=u.getUsername()%></td>
<td>
<a href="UserEditServlet?id=<%=u.getId()%>">编辑</a>
<a href="UserDeleteServlet?id=<%=u.getId()%>">删除</a>
</td>
</tr>
<% } %>
</table>

修改（userEdit.jsp）

<%@ page import="entity.User" %>
<%
User u = (User)request.getAttribute("user");
%>
<form action="UserEditServlet" method="post">
<input type="hidden" name="id" value="<%=u.getId()%>">
用户名：<input name="username" value="<%=u.getUsername()%>"><br>
密码：<input name="password" value="<%=u.getPassword()%>"><br>
<button>保存</button>
</form>

九、完整流程（答辩直接背）

1️⃣ JSP 提供界面
2️⃣ Servlet 接收请求
3️⃣ DAO 操作 MySQL
4️⃣ ResultSet → Java 对象
5️⃣ JSP 展示数据
6️⃣ Session 管理登录状态

十、如果你要「直接交作业」

我可以帮你👇
✔ 升级成 JSTL + EL（去 Scriptlet）
✔ 加动态背景 + 美化页面
✔ 写课程设计报告（8000 字）
✔ 打包 IDEA / Eclipse 项目
✔ 加登录拦截器 Filter