@Autowired
private BrandMapper brandMapper;
以上代码brandMapper经常爆红，程序却能正常运行，经度娘搜索后得出完美解决方案。网址链接：https://blog.csdn.net/Coder_Knight/article/details/83999139
Mapper文件中添加@Repository注解。
例如
@Repository
public interface BrandMapper extends Mapper<Brand> {
}
原文：https://www.cnblogs.com/nxxam/p/13288474.html