用Java实现用户页面的增、删、改，完成3种提交操作，增，删，改，把握好数据流，从jsp到servlet，再到mysql，体验MVC的整体架构， 2.挑战任务：完成用户页面的查询操作

好的，对于用户页面的增删改查操作，我们可以采用MVC架构，具体实现流程如下：

1. 数据库设计

首先，我们需要设计数据库，这里以用户表为例，设计如下：

CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `gender` varchar(10) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

2. 实体类设计

接着，我们需要设计实体类，这里我们创建一个User类，包含id、name、age、gender四个属性，以及对应的get/set方法。

public class User {
    private int id;
    private String name;
    private int age;
    private String gender;

    // 省略get/set方法
}

3. DAO层设计

接下来，我们需要设计DAO层，这里我们创建一个UserDao类，包含增删改查四个方法。

public class UserDao {
    // 数据库连接
    private Connection conn;

    // 构造方法，获取数据库连接
    public UserDao() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 增加用户
    public void addUser(User user) {
        try {
            String sql = "INSERT INTO user(name, age, gender) VALUES(?, ?, ?)";
            PreparedStatement pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, user.getName());
            pstmt.setInt(2, user.getAge());
            pstmt.setString(3, user.getGender());
            pstmt.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 删除用户
    public void deleteUser(int id) {
        try {
            String sql = "DELETE FROM user WHERE id=?";
            PreparedStatement pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1, id);
            pstmt.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 修改用户
    public void updateUser(User user) {
        try {
            String sql = "UPDATE user SET name=?, age=?, gender=? WHERE id=?";
            PreparedStatement pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, user.getName());
            pstmt.setInt(2, user.getAge());
            pstmt.setString(3, user.getGender());
            pstmt.setInt(4, user.getId());
            pstmt.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 查询用户
    public List<User> queryUser() {
        List<User> userList = new ArrayList<User>();
        try {
            String sql = "SELECT * FROM user";
            PreparedStatement pstmt = conn.prepareStatement(sql);
            ResultSet rs = pstmt.executeQuery();
            while (rs.next()) {
                User user = new User();
                user.setId(rs.getInt("id"));
                user.setName(rs.getString("name"));
                user.setAge(rs.getInt("age"));
                user.setGender(rs.getString("gender"));
                userList.add(user);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return userList;
    }
}

4. 控制器设计

接下来，我们需要设计控制器，这里我们创建一个UserServlet类，处理用户请求，并调用DAO层的方法进行增删改查操作。

public class UserServlet extends HttpServlet {
    private UserDao userDao = new UserDao();

    // 处理GET请求
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String action = request.getParameter("action");
        if (action.equals("add")) {
            addUser(request, response);
        } else if (action.equals("delete")) {
            deleteUser(request, response);
        } else if (action.equals("update")) {
            updateUser(request, response);
        } else if (action.equals("query")) {
            queryUser(request, response);
        }
    }

    // 处理POST请求
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    // 增加用户
    private void addUser(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        int age = Integer.parseInt(request.getParameter("age"));
        String gender = request.getParameter("gender");
        User user = new User();
        user.setName(name);
        user.setAge(age);
        user.setGender(gender);
        userDao.addUser(user);
        response.sendRedirect("user.jsp");
    }

    // 删除用户
    private void deleteUser(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        userDao.deleteUser(id);
        response.sendRedirect("user.jsp");
    }

    // 修改用户
    private void updateUser(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        String name = request.getParameter("name");
        int age = Integer.parseInt(request.getParameter("age"));
        String gender = request.getParameter("gender");
        User user = new User();
        user.setId(id);
        user.setName(name);
        user.setAge(age);
        user.setGender(gender);
        userDao.updateUser(user);
        response.sendRedirect("user.jsp");
    }

    // 查询用户
    private void queryUser(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<User> userList = userDao.queryUser();
        request.setAttribute("userList", userList);
        request.getRequestDispatcher("user.jsp").forward(request, response);
    }
}

5. 视图设计

最后，我们需要设计用户界面，这里我们创建一个user.jsp页面，包含增删改查四个操作。

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>用户管理</title>
</head>
<body>
    <h1>用户管理</h1>
    <form action="UserServlet" method="post">
        <input type="hidden" name="action" value="add">
        <p>姓名：<input type="text" name="name"></p>
        <p>年龄：<input type="text" name="age"></p>
        <p>性别：<input type="text" name="gender"></p>
        <p><input type="submit" value="增加"></p>
    </form>
    <table border="1">
        <tr>
            <th>ID</th>
            <th>姓名</th>
            <th>年龄</th>
            <th>性别</th>
            <th>操作</th>
        </tr>
        <c:forEach var="user" items="${userList}">
            <tr>
                <td>${user.id}</td>
                <td>${user.name}</td>
                <td>${user.age}</td>
                <td>${user.gender}</td>
                <td>
                    <a href="UserServlet?action=delete&id=${user.id}">删除</a>
                    <a href="update.jsp?id=${user.id}">修改</a>
                </td>
            </tr>
        </c:forEach>
    </table>
</body>
</html>

以上就是用户页面的增删改查操作的实现流程。如果要实现查询操作，只需要在user.jsp页面中添加查询表单和查询按钮，并在UserServlet类中添加queryUser()方法即可。