[Spring] Annotation Autowiring and Qualifiers

Autowiring 과 Qualifiers는 무엇인가?

Autowiring

• Injecting a Coach implementation

• Spring will scan @Components

• Any one implements Coach interface??

• If so, let’s inject them… but.. which one?

Multiple Coach Implementations

• 다양한 Coach Implementation 이 존재하면 어떻게 될까?

• 오류발생함 -> 왜냐하면 Spring이 뭘 선택해야할지 모름

Solution: Be specific! - @Qualifer

For Constructor Injection

@RestController
public class DemoController {

    private Coach myCoach;

    @Autowired
    public DemoController(@Qualifier("cricketCoach") Coach theCoach){
        myCoach = theCoach;
} //Coach 앞에 @Qualifier("클래스 이름") 주입.

    @GetMapping("/dailyworkout")
    public String getDailyWorkout() {
        return myCoach.getDailyWorkout();
}
}

• Specific the bean id: cricketCoach

• 이 bean id 는 CricketCoach와 같은 이름이면서 소문자 로 시작하면 된다.
• Other bean ids we could use: baseballCoach, trackCoach, tennisCoach..

For Setter Injection

• If you are using Setter injection, can also apply @Qualifier annotation

  @RestController
  public class DemoController {
    
      private Coach myCoach;
    
      @Autowired
      public void setCoach(@Qualifier("cricketCoach") Coach theCoach){
          myCoach = theCoach;
  } //@Qualifier 똑같이 사용
    
      @GetMapping("/dailyworkout")
      public String getDailyWorkout() {
          return myCoach.getDailyWorkout();
  }
  }
  

• Give bean id : cricketCoach with starting lower-case
• Other bean ids we could use: baseballCoach, trackCoach, tennisCoach..