一、定义实体类（Entity）：

// User.java
public class User {
private Long id;
private String username;
private String email;

// Getters and setters
}

二、创建Mapper接口：

// UserMapper.java
import java.util.List;

public interface UserMapper {
List<User> getAllUsers();
User getUserById(Long id);
void insertUser(User user);
void updateUser(User user);
void deleteUser(Long id);
}

三、创建Mapper XML文件：（在resources目录下创建一个与Mapper接口同名的XML文件，定义SQL语句）：

<!-- UserMapper.xml -->
<mapper namespace="com.example.mapper.UserMapper">
<select id="getAllUsers" resultType="com.example.model.User">
SELECT * FROM users;
</select>

<select id="getUserById" parameterType="Long" resultType="com.example.model.User">
SELECT * FROM users WHERE id = #{id};
</select>

<insert id="insertUser" parameterType="com.example.model.User">
INSERT INTO users (username, email) VALUES (#{username}, #{email});
</insert>

<update id="updateUser" parameterType="com.example.model.User">
UPDATE users SET username = #{username}, email = #{email} WHERE id = #{id};
</update>

<delete id="deleteUser" parameterType="Long">
DELETE FROM users WHERE id = #{id};
</delete>
</mapper>

四、创建Service接口和实现类：（实现类记得写@Service）：

// UserService.java
public interface UserService {
List<User> getAllUsers();
User getUserById(Long id);
void saveUser(User user);
void updateUser(User user);
void deleteUser(Long id);
}

// UserServiceImpl.java
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class UserServiceImpl implements UserService {
private final UserMapper userMapper;

@Autowired
public UserServiceImpl(UserMapper userMapper) {
this.userMapper = userMapper;
}

@Override
public List<User> getAllUsers() {
return userMapper.getAllUsers();
}

@Override
public User getUserById(Long id) {
return userMapper.getUserById(id);
}

@Override
public void saveUser(User user) {
userMapper.insertUser(user);
}

@Override
public void updateUser(User user) {
userMapper.updateUser(user);
}

@Override
public void deleteUser(Long id) {
userMapper.deleteUser(id);
}
}

五、创建Controller：（用于处理HTTP请求）：

// UserController.java
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
@RequestMapping("/api/users")
public class UserController {
private final UserService userService;

@Autowired
public UserController(UserService userService) {
this.userService = userService;
}

@GetMapping
public List<User> getAllUsers() {
return userService.getAllUsers();
}

@GetMapping("/{id}")
public User getUserById(@PathVariable Long id) {
return userService.getUserById(id);
}

@PostMapping
public void saveUser(@RequestBody User user) {
userService.saveUser(user);
}

@PutMapping("/{id}")
public void updateUser(@PathVariable Long id, @RequestBody User user) {
user.setId(id);
userService.updateUser(user);
}

@DeleteMapping("/{id}")
public void deleteUser(@PathVariable Long id) {
userService.deleteUser(id);
}
}