[스프링| 스프링 핵심 원리 | 기본편 | 의존관계 자동 주입] 다양한 의존관계 주입 방법

@Component
public class OrderServiceImpl implements OrderService {

    private final MemberRepository memberRepository;
    private final DiscountPolicy discountPolicy;

    @Autowired
    public OrderServiceImpl(MemberRepository memberRepository, DiscountPolicy discountPolicy) {
        this.memberRepository = memberRepository;
        this.discountPolicy = discountPolicy;
    }

    @Override
    public Order createOrder(Long memberId, String itemName, int itemPrice) {
        Member member = memberRepository.findById(memberId);
        int discountPrice = discountPolicy.discount(member, itemPrice);

        return new Order(memberId, itemName, itemPrice, discountPrice);
    }
}

중요! 생성자가 딱 1개만 있으면 @Autowired를 생략해도 자동 주입 된다.  물론 스프링 빈에만 해당한다.

@Component
public class OrderServiceImpl implements OrderService {
    private MemberRepository memberRepository;
    private DiscountPolicy discountPolicy;
    @Autowired
    public void setMemberRepository(MemberRepository memberRepository) {
        this.memberRepository = memberRepository;
    }
    @Autowired
    public void setDiscountPolicy(DiscountPolicy discountPolicy) {
        this.discountPolicy = discountPolicy;
    }
}

 

참고: 어쩌면 당연한 이야기이지만 의존관계 자동 주입은 스프링 컨테이너가 관리하는 스프링 빈이어야 동작한다. 스프링 빈이 아닌 `Member` 같은 클래스에서 `@Autowired` 코드를 적용해도 아무 기능도 동작하지 않는다.

//호출 안됨
@Autowired(required = false)
public void setNoBean1(Member member) {
     System.out.println("setNoBean1 = " + member);
 }

//null 호출
@Autowired
public void setNoBean2(@Nullable Member member) {
     System.out.println("setNoBean2 = " + member);
 }

//Optional.empty 호출
@Autowired(required = false)
public void setNoBean3(Optional<Member> member) {
 System.out.println("setNoBean3 = " + member);
 }