package com.example.demo;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@MapperScan("com.example.demo.mapper")
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

}

package com.example.demo.controller;

import com.example.demo.entity.User;
import com.example.demo.service.UserService;
import org.springframework.web.bind.annotation.*;

import java.util.List;

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

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

    @PostMapping
    public String add(@RequestBody User user) {
        userService.add(user);
        return "add success";
    }

    @DeleteMapping("/{id}")
    public String delete(@PathVariable Long id) {
        userService.delete(id);
        return "delete success";
    }

    @PutMapping
    public String update(@RequestBody User user) {
        userService.update(user);
        return "update success";
    }

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

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

package com.example.demo.mapper;

import com.example.demo.entity.User;
import org.apache.ibatis.annotations.*;

import java.util.List;

public interface UserMapper {
    @Insert("INSERT INTO user(name, age) VALUES(#{name}, #{age})")
    int insert(User user);

    @Delete("DELETE FROM user WHERE id = #{id}")
    int deleteById(Long id);

    @Update("UPDATE user SET name = #{name}, age = #{age} WHERE id = #{id}")
    int update(User user);

    @Select("SELECT * FROM user WHERE id = #{id}")
    User selectById(Long id);

    @Select("SELECT * FROM user")
    List<User> selectAll();
}

UserService.java

package com.example.demo.service;

import com.example.demo.entity.User;
import com.example.demo.mapper.UserMapper;
import org.springframework.stereotype.Service;

import java.util.List;
@Service
public class UserService {

    private final UserMapper userMapper;

    public UserService(UserMapper userMapper) {
        this.userMapper = userMapper;
    }

    public int add(User user) {
        return userMapper.insert(user);
    }

    public int delete(Long id) {
        return userMapper.deleteById(id);
    }

    public int update(User user) {
        return userMapper.update(user);
    }

    public User getById(Long id) {
        return userMapper.selectById(id);
    }

    public List<User> getAll() {
        return userMapper.selectAll();
    }
}

User.java

package com.example.demo.entity;

import lombok.Data;

@Data
public class User {
    private Long id;
    private String name;
    private Integer age;
}