Bean with Component Scan(2)

💡 How to add Bean

• @Bean등록하는 방법
• 1️⃣ manual bean configuration with @Configuration
• 2️⃣ component scan with @ComponentScan, @Autowired
• 이 게시글에서는 2️⃣번 방법에 대해 설명

✅ Component Scan

• Spring does not magically know what to add as bean ➡️ scans your project marked as bean

• this scanning is called: @Component Scan

• @Component Scan은 @Component 어노테이션이 붙은 클래스는 모두 Spring Bean으로 알아서 등록한다.
  • @Component
  • @Controller
  • @Service
  • @Repository
  • @Configuration
• 의존성 주입: @Autowired

• @Autowired가 붙은 생성자는 자동으로 해당 Spring Bean을 찾아서 의존성을 주입한다.

• 1️⃣ (before)manual bean configuration
• Bean으로 등록하고 싶은 클래스들을 AppConfig에 명시해야 했음

@Configuration
public class AppConfig {

    @Bean
    public MemberService memberService(){
        return new MemberServiceImpl(memberRepository());
    }

    @Bean
    public OrderService orderService(){
        return new OrderServiceImpl(
                memberRepository(),
                discountPolicy());
    }
}

• 2️⃣ component scan with @ComponentScan
• 이제 config피일은 텅텅 비었다!
• @ComponentScan은 @Component가 붙은 클래스를 찾아 spring bean으로 등록한다.

@Configuration
@ComponentScan
public class AutoAppConfig {}

• 그리고 bean으로 등록하고 싶은 구체 클래스에 @Component를 붙인다.
• 그리고 @Autowired가 붙은 메소드를 자동으로 의존성을 주입한다.

@Component //자동으로 spring bean등록
public class OrderServiceImpl implements OrderService {
    private final MemberRepository repository;
    private final DiscountPolicy discountPolicy;

    @Autowired //자동으로 의존성 주입
    public OrderServiceImpl(MemberRepository repository, DiscountPolicy discountPolicy) {
        this.repository = repository;
    }

@Component  //자동으로 spring bean등록
public class MemberServiceImpl implements MemberService{
    private final MemberRepository memberRepository;

    @Autowired //자동으로 의존성 주입
    public MemberServiceImpl(MemberRepository memberRepository) {
        this.memberRepository = memberRepository;
    }
}

@Component //자동으로 spring bean등록
public class OrderServiceImpl implements OrderService {
}

✅ Component Scan 범위 지정하기

• place config file in root of project file
• basePackages: search below this package
• excludeFilters: do not add this class as bean

@Configuration
@ComponentScan(
        basePackages = "com.example.spring_basic",
        excludeFilters = @ComponentScan.Filter(type = FilterType.ANNOTATION, classes = Configuration.class )
)
public class AutoAppConfig { }

✅ Filter

• filter what/what not to include in component scan
• includeFilters
• excludeFilters

@Configuration
@ComponentScan(
        includeFilters =  @ComponentScan.Filter(type = FilterType.ANNOTATION, classes = MyIncludeComponent.class),
        excludeFilters =  @ComponentScan.Filter(type = FilterType.ANNOTATION, classes = MyExcludeComponent.class))
static class ComponentFilterAppConfig{
    }

❓ Bean duplication, bean collision

• ❓ What happens if bean names are identical?
• 컴포넌트 스캔에 의해 자동으로 스프링 빈이 등록되는데, 그 이름이 같은 경우 스프링은 오류 발생 시킴

• 🔴 ConflictingBeanDefinitionException 예외 발생

• ❓ What happens if bean is added both manually and auto with component scan?
• There are two ways of adding bean
• 1️⃣ manual bean configuration with @Configuration
• 2️⃣ component scan with @ComponentScan

• 두 방법 모두으로 같은 bean이 두 번 등록된다면?

• 1️⃣ manual bean configuration has priority
• manual bean overrides component scan
• 🔴 그러나 권장하는 방법이 아니며, Springboot는 최근에 오류를 발생시키도록 바뀜

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