【mybatis】-- springboot整合mybatis

<dependency>
     <groupId>org.mybatis.spring.boot</groupId>
     <artifactId>mybatis-spring-boot-starter</artifactId>
     <version>2.0.0</version>
</dependency>

spring.datasource.type=com.alibaba.druid.pool.DruidDataSource
spring.datasource.url=jdbc:mysql://localhost:3306/Take_Lessons?serverTimezone=UTC&characterEncoding=UTF-8
spring.datasource.username=root
spring.datasource.password=xxxxx

CREATE TABLE `User` (
   `user_id` int(4) NOT NULL,
   `user_name` varchar(15) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL COMMENT ‘用户姓名‘,
   `user_identify` int(2) DEFAULT NULL COMMENT ‘用户身份‘,
   `salt` varchar(20) DEFAULT NULL COMMENT ‘盐‘,
   `user_number` varchar(20) DEFAULT NULL COMMENT ‘用户学号或工号‘,
   `user_grade` varchar(5) DEFAULT NULL COMMENT ‘学生年级‘,
   `user_major` varchar(30) DEFAULT NULL COMMENT ‘学生专业‘,
   PRIMARY KEY (`user_id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci

public class User {

    private int id;
    private String user_name;
    private String salt;
    private int user_identify;
    private String user_number;
    private String user_grade;
    private String user_major;
    
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUser_name() {
        return user_name;
    }

    public void setUser_name(String user_name) {
        this.user_name = user_name;
    }

    public String getSalt() {
        return salt;
    }

    public void setSalt(String salt) {
        this.salt = salt;
    }

    public int getUser_identify() {
        return user_identify;
    }

    public void setUser_identify(int user_identify) {
        this.user_identify = user_identify;
    }

    public String getUser_number() {
        return user_number;
    }

    public void setUser_number(String user_number) {
        this.user_number = user_number;
    }

    public String getUser_grade() {
        return user_grade;
    }

    public void setUser_grade(String user_grade) {
        this.user_grade = user_grade;
    }

    public String getUser_major() {
        return user_major;
    }

    public void setUser_major(String user_major) {
        this.user_major = user_major;
    }

    public User() {
        // TODO Auto-generated constructor stub
    }
    
}

@Mapper
public interface UserDao {

    @Select("select * from User where user_id = #{id}")
    public User getById(@Param("id")int id);
    
    
}

@Service
public class UserService {

    @Autowired
    UserDao userDao;
    
    public User getById(int id){
        return userDao.getById(id);
    }

}

@ResponseBody
    @GetMapping("/user")
    public Result<User> user(){
        User user=userService.getById(1);
        return Result.success(user);
    }