@Service
public class UserService {
        @Autowired
        private UserMapper userMapper;

        public List<User> queryAll(){
            System.out.println("热部署");
            return userMapper.findAll();
        }
    @Transactional
    public void deleteById(Integer id) {
           userMapper.deleteById(id);
         //  int c=10/0;
    }
}

@SpringBootApplication
@EnableTransactionManagement //开启事务管理注解模式 最新的版本可以省略
@MapperScan("com.xz.springboot.mapper") //扫描该包下所有的接口并为该接口生成实现类
public class Springboot01Application {

    public static void main(String[] args) {
        SpringApplication.run(Springboot01Application.class, args);
    }

}