빈 연결: @Component, @Service, @Repository

스테레오타입 애너테이션

@Component: 일반 빈

@Component
public class EmailFormatter {
    public String format(String to, String subject) {
        return "To: " + to + "\nSubject: " + subject;
    }
}

@Service: 비즈니스 로직 계층

@Service
public class OrderService {
    private final OrderRepository repo;
    public OrderService(OrderRepository repo) { this.repo = repo; }
    public Order placeOrder(Cart cart) { /* business logic */ return repo.save(new Order(cart)); }
}

@Repository: 데이터 액세스 계층

@Repository
public class JdbcUserRepository {
    private final JdbcTemplate jdbc;
    public JdbcUserRepository(JdbcTemplate jdbc) { this.jdbc = jdbc; }
    public User findById(long id) {
        return jdbc.queryForObject("SELECT * FROM users WHERE id=?",
            new BeanPropertyRowMapper<>(User.class), id);
    }
}

@Configuration 클래스의 @Bean

@Configuration
public class AppConfig {
    @Bean
    public ObjectMapper objectMapper() {
        return new ObjectMapper().registerModule(new JavaTimeModule());
    }
    @Bean
    public RestTemplate restTemplate() { return new RestTemplate(); }
}

컴포넌트 스캔

// Explicit scan (rarely needed in Spring Boot):
@SpringBootApplication
@ComponentScan(basePackages = {"com.example.app", "com.example.shared"})
public class MyApp { ... }

빈 이름 지정

@Service("orderSvc")
public class OrderService { ... }
// Inject by name:
@Autowired @Qualifier("orderSvc")
private OrderService svc;

빈 범위

@Service
@Scope("prototype")
public class ReportBuilder {
    private List<String> lines = new ArrayList<>();
    public void addLine(String line) { lines.add(line); }
}

모호성 해결을 위한 @Primary와 @Qualifier

@Service @Primary
public class CacheUserService implements UserService { ... }
@Service
public class DbUserService implements UserService { ... }
// Inject specific one:
@Autowired @Qualifier("dbUserService")
private UserService userService;

지연 초기화

@Service @Lazy
public class HeavyReportService {
    public HeavyReportService() { System.out.println("Created on first use"); }
}

@PostConstruct와 @PreDestroy

@Service
public class CacheService {
    @PostConstruct
    public void init() { System.out.println("Cache warming up..."); }
    @PreDestroy
    public void cleanup() { System.out.println("Cache cleared."); }
}

간단한 확인

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