第三步，service业务层接口和实现类模版

接口模版

package com.tj.reggie.service;
import com.baomidou.mybatisplus.extension.service.IService;
import com.tj.reggie.entity.Users;
public interface UsersService extends IService<Users> {
    //业务层接口继承
}

实现类模版

package com.tj.reggie.service.impl;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.tj.reggie.entity.Users;
import com.tj.reggie.mapper.UsersMapper;
import com.tj.reggie.service.UsersService;
import org.springframework.stereotype.Service;
@Service
public class UsersServiceImpl extends ServiceImpl<UsersMapper, Users> implements UsersService {
    //继承ServiceImpl<UsersMapper, Users>，第一个填Mapper方法,第二实现类
    //实现UsersService接口
    //这个地方是写业务层的逻辑的，都是先定义接口，然后再写实现类
}