DDD, Hexagonal Architecture를 활용한 Backend 구조 표준

package com.company.project.order.domain.model;

import lombok.Getter;

@Getter
public class Order { // POJO
    private final Long id;
    private final String product;
    private OrderStatus status;

    // 생성자 및 비즈니스 로직
    public void complete() {
        if (this.status == OrderStatus.CANCELED) {
            throw new IllegalStateException("이미 취소된 주문입니다.");
        }
        this.status = OrderStatus.COMPLETED;
    }
}

package com.company.project.order.application.port.in;

public interface CreateOrderUseCase {
    Long createOrder(CreateOrderCommand command);
}

package com.company.project.order.application.service;

import com.company.project.order.application.port.in.CreateOrderUseCase;
import com.company.project.order.domain.model.Order;
import com.company.project.order.domain.repository.OrderRepository;
import lombok.RequiredArgsConstructor;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

@Service
@RequiredArgsConstructor
public class CreateOrderService implements CreateOrderUseCase {

    private final OrderRepository orderRepository; // Domain의 인터페이스 의존

    @Override
    @Transactional
    public Long createOrder(CreateOrderCommand command) {
        Order order = Order.create(command.getProduct()); // 도메인 로직 호출
        orderRepository.save(order);
        return order.getId();
    }
}

// 1. JPA Entity (DB 테이블 매핑용)
@Entity
@Table(name = "orders")
class OrderJpaEntity { 
    @Id @GeneratedValue
    private Long id;
    private String product;
    // ...
}

// 2. Spring Data JPA
interface OrderJpaRepository extends JpaRepository<OrderJpaEntity, Long> {}

// 3. Adapter 구현체 (Domain Repository 인터페이스 구현)
@Component
@RequiredArgsConstructor
public class OrderPersistenceAdapter implements OrderRepository {

    private final OrderJpaRepository jpaRepository;

    @Override
    public void save(Order order) {
        // Domain Entity -> JPA Entity 변환 (Mapper 사용 권장)
        OrderJpaEntity entity = toJpaEntity(order);
        jpaRepository.save(entity);
    }
    
    @Override
    public Order findById(Long id) {
         // JPA Entity -> Domain Entity 변환 후 리턴
         return jpaRepository.findById(id).map(this::toDomain).orElseThrow();
    }
}