Ch07. 의존관계 자동 주입 - 조회한 빈이 모두 필요할 때(List, Map)

• 의도적으로 정말 해당 타입의 스프링 빈이 다 필요한 경우도 있다. 
• 예를 들어서 할인 서비스를 제공하는데, 클라이언트가 할인의 종류(rate, fix)를 선택할 수 있다고 가정해보자. 스프링을 사용하면 소위 말하는 전략 패턴을 매우 간단하게 구현할 수 있다.

• public class AllBeanTest {
  
      @Test
      public void findAllBean(){
          ApplicationContext applicationContext = new AnnotationConfigApplicationContext(
              AutoAppConfig.class, DiscountService.class);
          DiscountService discountService = applicationContext.getBean(DiscountService.class);
          Member member = new Member(1L, "userA", Grade.VIP);
          int discountPrice = discountService.discount(member, 10000, "fixDiscountPolicy");
          assertThat(discountService).isInstanceOf(DiscountService.class);
          assertThat(discountPrice).isEqualTo(1000);
  
          int rateDiscountPolicy = discountService.discount(member, 20000, "rateDiscountPolicy");
          assertThat(rateDiscountPolicy).isEqualTo(2000);
  
      }
  
      static class DiscountService{
          private final Map<String, DiscountPolicy> policyMap;
          private final List<DiscountPolicy> policies;
  
          @Autowired
          public DiscountService(
              Map<String, DiscountPolicy> policyMap,
              List<DiscountPolicy> policies) {
              this.policyMap = policyMap;
              this.policies = policies;
              System.out.println("policyMap = " + policyMap);
              System.out.println("policies = " + policies);
          }
  
          public int discount(Member member, int price, String discountCode) {
              DiscountPolicy discountPolicy = policyMap.get(discountCode);
              return discountPolicy.discount(member, price);
          }
      }
  }

  
  
  • 로직 분석
    • DiscountService는 Map으로 모든 DiscountPolicy를 주입받는다. 이때 fixDiscountPolicy, rateDiscountPolicy가 주입된다. 
    • discount ()메서드는 discountCode로 "fixDiscountPolicy"가 넘어오면 map에서 fixDiscountPolicy 스프링 빈을 찾아서 실행한다. 물론 “rateDiscountPolicy”가 넘어오면 rateDiscountPolicy 스프링 빈을 찾아서 실행한다.
  • 주입 분석
    •  Map<String, DiscountPolicy>: map의 키에 스프링 빈의 이름을 넣어주고, 그 값으로 DiscountPolicy 타입으로 조회한 모든 스프링 빈을 담아준다. 
    • List <DiscountPolicy>: DiscountPolicy 타입으로 조회한 모든 스프링 빈을 담아준다. 만약 해당하는 타입의 스프링 빈이 없으면, 빈 컬렉션이나 Map을 주입한다.