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实体类不变：

package org.example.Entity;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;

@TableName("users")        //不一致时，需要映射
public class MyUser
{
    @TableId(type = IdType.AUTO)
    private int id;

    private String name;

    private int age;

    public int getId()
    {

        return id;
    }

    public void setId(int id)
    {

        this.id = id;
    }

    public String getName()
    {

        return name;
    }

    public void setName(String name)
    {

        this.name = name;
    }

    public int getAge()
    {

        return age;
    }

    public void setAge(int age)
    {

        this.age = age;
    }

    @Override
    public String toString()
    {

        return "MyUser{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

服务类：

package org.example.service;

import org.example.Entity.MyUser;

import java.util.List;

public interface MyUserService
{

    // 查询所有用户
    List<MyUser> findAll();

    int save(MyUser myUser);


    int update(MyUser myUser);

}

package org.example.service.Impl;

import org.example.Entity.MyUser;
import org.example.mapper.UserMapper;
import org.example.service.MyUserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;

@Service
public class MyUserServiceImpl implements MyUserService
{

    //继承了BaseMapper所有的方法，可以编写自己的扩展方法
    @Autowired
    private UserMapper userMapper;


    /**
     * 查询所有用户信息
     * @return
     */
    @Override
    public List<MyUser> findAll()
    {

        return userMapper.selectList(null);


    }

    /**
     * 增加一个用户信息
     * @param myUser
     * @return
     */
    @Override
    public int save(MyUser myUser) {
        return userMapper.insert(myUser);
    }

    /**
     * 通过id修改用户信息
     * @param myUser
     * @return
     */
    @Override
    public int update(MyUser myUser) {
        return userMapper.updateById(myUser);
    }


}

控制器类：

package org.example.controller;

import org.example.Entity.MyUser;
import org.example.service.MyUserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import java.util.List;

@RestController
public class MyUserController
{

    @Autowired
    private MyUserService myUserService;


    @GetMapping(value = "/findAll")
    public List<MyUser> findAll()
    {
        // 查询所有用户信息
        List<MyUser> users = myUserService.findAll();

        for (MyUser user : users)
        {
            System.out.println(user.getId()+"  "+user.getName()+"  "+user.getAge());
        }

        return users;
    }


    @GetMapping(value = "/save")
    public int save()
    {
        MyUser user = new MyUser();
        user.setName("小文");
        user.setAge(21);

        int insert = myUserService.save(user);//如果没有设置id，那么会自动生成id

        System.out.println(insert);//受影响行数

        System.out.println(user);//id会自动回填

        return insert;
    }

    @GetMapping(value = "/updateById")
    public int updateById()
    {
        MyUser user = new MyUser();
        user.setId(1014);
        user.setName("小文改");
        user.setAge(222);

        int insert = myUserService.update(user);

        System.out.println(insert);//受影响行数


        return insert;
    }


}