使用Spring Boot实现操作数据库的接口的过程

@Getter @Setter
public class User {
    private int id;
    private String username;
    private String password;
    private int age;
}

@Repository
public interface UserDao {
    public User getUserById(@Param("id") int id);
    public List<User> getUserByAge(@Param("age") int age);
    public List<User> getUserByName(@Param("username") String username);
    public int insertUser(@RequestBody User user);

}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.demo.dao.UserDao">
    <select id="getUserById" resultType="User">
        select * from `user` where id=#{id}
    </select>
    <select id="getUserByAge" resultType="User">
        select * from `user` where age=#{age}
    </select>
    <select id="getUserByName" resultType="User">
        select * from `user` where username like concat('%',#{username},'%')
    </select>

    <insert id="insertUser" parameterType="User">
        <selectKey keyProperty="id" order="AFTER" resultType="int">
            SELECT LAST_INSERT_ID()
        </selectKey>
        insert into user (username, password, age)
        values (#{username,jdbcType=VARCHAR}, #{password,jdbcType=VARCHAR}, #{age,jdbcType=INTEGER})
    </insert>
</mapper>

public interface UserService {
    public User queryUserById(int id);
    public List<User> queryUserByAge(int age);
    public List<User> queryUserByName(String username);
    public int insertUser(User user);
}

@Service
public class UserSeviceImpl implements UserService {
    @Autowired
    private UserDao userDao;

    @Override
    public User queryUserById(int id) {
        return userDao.getUserById(id);
    }

    @Override
    public List<User> queryUserByAge(int age) {
        return userDao.getUserByAge(age);
    }

    @Override
    public List<User> queryUserByName(String username) {
        return userDao.getUserByName(username);
    }

    @Override
    public int insertUser(User user) {
        return userDao.insertUser(user);
    }
}

@RestController
public class UserController {

    @Autowired
    private UserService userService;

    @GetMapping("/userid")
    public User getUserById(@RequestParam("id") int id){
        return userService.queryUserById(id);
    }

    @GetMapping("/username")
    public List<User> getUserByUsername(@RequestParam("username") String username){
        return userService.queryUserByName(username);
    }

    @RequestMapping(value="/insert",method = RequestMethod.POST)
    public User insertUser(@RequestBody User user){
        int x = userService.insertUser(user);
        return user;
    }
}

server:
  port: 8080
spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/testingdev9?useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai
    username: root
    password: 123456
mybatis:
  mapper-locations:
    - classpath:mapper/*.xml
    - classpath*:com/**/mapper/*.xml
  type-aliases-package: com.example.demo.model