當一個接口有多個實現類,假如說DownloadServiceImlp1,DownloadServiceImlp2都實現了DownloadService,那麼在Download業務的controller中註冊Service服務時就會用到@Qualifier註解
@Autowired
@Qualifier("downloadSeriveImpl1") //這裏註解的值是service實現類中@service註解值之一
private DownloadService service;
還可參考https://blog.csdn.net/qq_36567005/article/details/80611139