spring boot写java web和接口

@RestController

public class Hello {
    @RequestMapping("/hello")
    public String hello(){
        return "helloworld";
    }

}

spring:
      datasource:
            driver-class-name: com.mysql.cj.jdbc.Driver
            url: jdbc:mysql://localhost:3306/student?useUnicode=true&useSSL=false&characterEncoding=utf8&serverTimezone=Asia/Shanghai
            username: root
            password: 123456
mybatis:
      mapper-locations: classpath:mapper/*.xml

@Data
public class User {
    private  int id ;
    private String name;
    private int age;
    private String email;
    *****

@Mapper
public interface UserMapper {
    List<User> findAll();
}

<?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.liuyang.mapper.UserMapper">
    <select id="findAll" resultType="com.liuyang.entity.User">
        SELECT * FROM user
    </select>
</mapper>

@RestController
public class UserController {

    @Autowired
    //把userService实例化
    private UserService userService;
    @RequestMapping("/user")
    public List<User> getUser(){

        return userService.findAll();

    }

}