Spring、Springboot常用注解：@Qualifier(不定時更新)

1、@Qualifier

出現場景：

老項目中有多個實現類實現同一個接口時，或者一個項目中有多個數據源時，spring容器不知道該注入哪個實現類或者使用哪個數據源，該注解就派上用場。

1）多實現類實現同一接口

//接口
public interface MemberService {
    public Member getMemberById(Long mid);
}
//實現類一
@Service("memberService1")
public class MemberServiceImpl1 implements MemberService{
    @Override
    public Member getMemberById(Long mid){
        //業務代碼1
    }
}
//實現類二
@Service("memberService2")
public class MemberServiceImpl2 implements MemberService{
    @Override
    public Member getMemberById(Long mid){
        //業務代碼2
    }
}
//調用類
@Controller("/member")
public class MemberController{
    @Autowired
    @Qualifier("memberService2") //此處如果不使用該注解則報錯，原因就是容器不知道注入哪一個實現類
    private MemberService memberService;
    
    @PostMapping(value = "/getMember",produces ={MediaType..APPLICATION_JSON_VALUE})
    public Response getMember(Long mid){
        return new Response().setDate(memberService.getMemberById(mid));
    }
}