新建一个类写入一下内容（其中定义的需要和数据表中的相对应）：

import java.util.Date;

public class User {
    /**
     * bigint > Long
     */
    private Long id;
    private String name;
    private String passwd;
    private String sex;
    private String phoneNum;

    private Date create_time;
    private Date update_time;

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPasswd() {
        return passwd;
    }

    public void setPasswd(String passwd) {
        this.passwd = passwd;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getPhoneNum() {
        return phoneNum;
    }

    public void setPhoneNum(String phoneNum) {
        this.phoneNum = phoneNum;
    }

    public Date getCreate_time() {
        return create_time;
    }

    public void setCreate_time(Date create_time) {
        this.create_time = create_time;
    }

    public Date getUpdate_time() {
        return update_time;
    }

    public void setUpdate_time(Date update_time) {
        this.update_time = update_time;
    }
}

在UserController中新建一个方法

@RequestMapping("/user")
    public User user(Long id){
        return userMapper.selectUserById(id);
    }

在UserMapper中加入以下内容：

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

在application.yml中顶格加入

mybatis:
  config-location:
    map-underscore-to-camel-case: true

然后访问http://127.0.0.1:8080/user?id=1可获取数据库中id为1的整条数据