컴포넌트 스캔

@Configuration
public class AppConfig {
    @Bean
    public MemberService memberService() { ... }

    @Bean
    public MemberRepository memberRepository() { ... }

    @Bean
    public OrderService orderService() { ... }

    @Bean
    public DiscountPolicy discountPolicy() { ... }

    // 빈이 수십, 수백 개가 되면?
    // 누락, 오타 위험 증가
}

@Configuration
@ComponentScan(
    excludeFilters = @ComponentScan.Filter(
        type = FilterType.ANNOTATION,
        classes = Configuration.class
    )  // 예제를 위해 기존 AppConfig 제외
)
public class AutoAppConfig {
    // @Bean 없이 자동으로 빈 등록!
}

@Component
public class MemoryMemberRepository implements MemberRepository {

    private static Map<Long, Member> store = new HashMap<>();

    @Override
    public void save(Member member) {
        store.put(member.getId(), member);
    }

    @Override
    public Member findById(Long memberId) {
        return store.get(memberId);
    }
}

@Component
public class RateDiscountPolicy implements DiscountPolicy {

    private int discountPercent = 10;

    @Override
    public int discount(Member member, int price) {
        if (member.getGrade() == Grade.VIP) {
            return price * discountPercent / 100;
        }
        return 0;
    }
}

@Component
public class MemberServiceImpl implements MemberService {

    private final MemberRepository memberRepository;

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

    // ...
}

@Component
public class OrderServiceImpl implements OrderService {

    private final MemberRepository memberRepository;
    private final DiscountPolicy discountPolicy;

    @Autowired  // 여러 파라미터도 자동 주입
    public OrderServiceImpl(MemberRepository memberRepository,
                           DiscountPolicy discountPolicy) {
        this.memberRepository = memberRepository;
        this.discountPolicy = discountPolicy;
    }

    // ...
}

@ComponentScan(
    basePackages = "hello.core"  // 이 패키지를 포함한 하위 패키지 모두 탐색
)

@ComponentScan(
    basePackages = {"hello.core", "hello.service"}  // 여러 시작 위치 지정
)

@ComponentScan(
    basePackageClasses = AutoAppConfig.class  // 이 클래스의 패키지가 시작 위치
)

// 프로젝트 최상단에 위치
@Configuration
@ComponentScan
public class AutoAppConfig {
    // basePackages 지정 없음 → 이 클래스의 패키지(hello.core)부터 탐색
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
    @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
    @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class)
})
public @interface SpringBootApplication {
    // ...
}

// @Controller 내부
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component  // @Component 포함!
public @interface Controller {
}

// @Service 내부
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component  // @Component 포함!
public @interface Service {
}

// @Repository 내부
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component  // @Component 포함!
public @interface Repository {
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface MyIncludeComponent {
    // 스캔 대상에 추가할 애노테이션
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface MyExcludeComponent {
    // 스캔 대상에서 제외할 애노테이션
}

@MyIncludeComponent
public class BeanA {
}

@MyExcludeComponent
public class BeanB {
}

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

@Test
void filterScan() {
    ApplicationContext ac = new AnnotationConfigApplicationContext(ComponentFilterAppConfig.class);

    BeanA beanA = ac.getBean("beanA", BeanA.class);
    assertThat(beanA).isNotNull();  // 등록됨

    assertThrows(NoSuchBeanDefinitionException.class,
        () -> ac.getBean("beanB", BeanB.class));  // 제외됨
}

// ASSIGNABLE_TYPE 예시
@ComponentScan(
    excludeFilters = @Filter(
        type = FilterType.ASSIGNABLE_TYPE,
        classes = BeanA.class
    )
)

// REGEX 예시
@ComponentScan(
    excludeFilters = @Filter(
        type = FilterType.REGEX,
        pattern = ".*Stub.*"
    )
)

// CUSTOM 예시
public class MyTypeFilter implements TypeFilter {
    @Override
    public boolean match(MetadataReader metadataReader,
                        MetadataReaderFactory metadataReaderFactory) {
        // true 반환 시 스캔 대상
        String className = metadataReader.getClassMetadata().getClassName();
        return className.contains("Exclude");
    }
}

@ComponentScan(
    excludeFilters = @Filter(
        type = FilterType.CUSTOM,
        classes = MyTypeFilter.class
    )
)

@Component("service")
public class MemberServiceImpl implements MemberService {
}

@Component("service")  // 같은 이름!
public class OrderServiceImpl implements OrderService {
}

@Component
public class MemoryMemberRepository implements MemberRepository {
}

@Configuration
@ComponentScan
public class AutoAppConfig {

    @Bean(name = "memoryMemberRepository")  // 같은 이름으로 수동 등록
    public MemberRepository memberRepository() {
        return new MemoryMemberRepository();
    }
}

# application.properties
spring.main.allow-bean-definition-overriding=true

# application.yml
spring:
  main:
    allow-bean-definition-overriding: true

@SpringBootApplication  // @ComponentScan 포함
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}

@SpringBootApplication
public class MyApplication implements CommandLineRunner {

    @Autowired
    private ApplicationContext applicationContext;

    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }

    @Override
    public void run(String... args) {
        String[] beanNames = applicationContext.getBeanDefinitionNames();
        for (String beanName : beanNames) {
            System.out.println("Bean: " + beanName);
        }
    }
}

@SpringBootApplication(
    scanBasePackages = {"com.example.myapp", "com.example.common"}
)
public class MyApplication {
    // ...
}