JavaWeb实现增删改查

JavaWeb实现增删改查一般需要以下步骤：

1. 编写数据库表结构
2. 编写JavaBean类，对应数据库表结构
3. 编写DAO层，实现增删改查操作
4. 编写Service层，调用DAO层实现业务逻辑
5. 编写Controller层，接收请求，调用Service层处理请求，返回响应

下面是一个简单的示例：

1. 编写数据库表结构

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 DEFAULT CHARSET=utf8;

2. 编写JavaBean类

public class User {
    private int id;
    private String name;
    private int age;
    private String gender;
    // 省略getter和setter方法
}

3. 编写DAO层

public class UserDao {
    private Connection conn;
    
    public UserDao(Connection conn) {
        this.conn = conn;
    }
    
    public void add(User user) {
        PreparedStatement pstmt = null;
        try {
            String sql = "INSERT INTO user(name, age, gender) VALUES (?, ?, ?)";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, user.getName());
            pstmt.setInt(2, user.getAge());
            pstmt.setString(3, user.getGender());
            pstmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            // 关闭资源
        }
    }
    
    public void delete(int id) {
        PreparedStatement pstmt = null;
        try {
            String sql = "DELETE FROM user WHERE id=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1, id);
            pstmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            // 关闭资源
        }
    }
    
    public void update(User user) {
        PreparedStatement pstmt = null;
        try {
            String sql = "UPDATE user SET name=?, age=?, gender=? WHERE id=?";
            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 (SQLException e) {
            e.printStackTrace();
        } finally {
            // 关闭资源
        }
    }
    
    public User getById(int id) {
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        User user = null;
        try {
            String sql = "SELECT * FROM user WHERE id=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1, id);
            rs = pstmt.executeQuery();
            if (rs.next()) {
                user = new User();
                user.setId(rs.getInt("id"));
                user.setName(rs.getString("name"));
                user.setAge(rs.getInt("age"));
                user.setGender(rs.getString("gender"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            // 关闭资源
        }
        return user;
    }
    
    public List<User> getAll() {
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        List<User> userList = new ArrayList<>();
        try {
            String sql = "SELECT * FROM user";
            pstmt = conn.prepareStatement(sql);
            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 (SQLException e) {
            e.printStackTrace();
        } finally {
            // 关闭资源
        }
        return userList;
    }
}

4. 编写Service层

public class UserService {
    private UserDao userDao;
    
    public UserService(UserDao userDao) {
        this.userDao = userDao;
    }
    
    public void add(User user) {
        userDao.add(user);
    }
    
    public void delete(int id) {
        userDao.delete(id);
    }
    
    public void update(User user) {
        userDao.update(user);
    }
    
    public User getById(int id) {
        return userDao.getById(id);
    }
    
    public List<User> getAll() {
        return userDao.getAll();
    }
}

5. 编写Controller层

public class UserController {
    private UserService userService;
    
    public UserController(UserService userService) {
        this.userService = userService;
    }
    
    public void add(HttpServletRequest request, HttpServletResponse response) {
        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);
        
        userService.add(user);
        
        // 返回响应
    }
    
    public void delete(HttpServletRequest request, HttpServletResponse response) {
        int id = Integer.parseInt(request.getParameter("id"));
        
        userService.delete(id);
        
        // 返回响应
    }
    
    public void update(HttpServletRequest request, HttpServletResponse response) {
        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);
        
        userService.update(user);
        
        // 返回响应
    }
    
    public void getById(HttpServletRequest request, HttpServletResponse response) {
        int id = Integer.parseInt(request.getParameter("id"));
        
        User user = userService.getById(id);
        
        // 返回响应
    }
    
    public void getAll(HttpServletRequest request, HttpServletResponse response) {
        List<User> userList = userService.getAll();
        
        // 返回响应
    }
}