주문과 할인 도메인 개발

1. 할인 정책 인터페이스
- src/main/java/hello/core/discount/DiscountPolicy.java

package hello.core.discount;

import hello.core.member.Member;

public interface DiscountPolicy {

    /**
     * @return 할인 대상 금액
     */
    int discount(Member member, int price);

}

2. 정액 할인 정책 구현체
- src/main/java/hello/core/discount/FixDiscountPolicy.java

package hello.core.discount;

import hello.core.member.Grade;
import hello.core.member.Member;

public class FixDiscountPolicy implements DiscountPolicy {

    private int discountFixAmount = 1000; // 1000원 할인

    @Override
    public int discount(Member member, int price) {
        if (member.getGrade() == Grade.VIP) { // Enum 타입에는 == 써야 함
            return discountFixAmount;
        } else {
            return 0;
        }
    }

}

VIP면 1000원 할인, 아니면 할인 없음


3. 주문 엔티티
- src/main/java/hello/core/order/Order.java

package hello.core.order;

public class Order {

    private Long memberId;
    private String itemName;
    private int itemPrice;
    private int discountPrice;

    public Order(Long memberId, String itemName, int itemPrice, int discountPrice) {
        this.memberId = memberId;
        this.itemName = itemName;
        this.itemPrice = itemPrice;
        this.discountPrice = discountPrice;
    }

    public int calculatePrice() {
        return itemPrice - discountPrice;
    }

    public Long getMemberId() {
        return memberId;
    }

    public String getItemName() {
        return itemName;
    }

    public int getItemPrice() {
        return itemPrice;
    }

    public int getDiscountPrice() {
        return discountPrice;
    }

    @Override
    public String toString() {
        return "Order{" +
                "memberId=" + memberId +
                ", itemName='" + itemName + '\'' +
                ", itemPrice=" + itemPrice +
                ", discountPrice=" + discountPrice +
                '}';
    }

}

4. 주문 서비스 인터페이스
- src/main/java/hello/core/order/OrderService.java

package hello.core.order;

public interface OrderService {

    Order createOrder(Long memberId, String itemName, int itemPrice);

}

5. 주문 서비스 구현체
- src/main/java/hello/core/order/OrderServiceImpl.java

package hello.core.order;

import hello.core.discount.DiscountPolicy;
import hello.core.discount.FixDiscountPolicy;
import hello.core.member.Member;
import hello.core.member.MemberRepository;
import hello.core.member.MemoryMemberRepository;

public class OrderServiceImpl implements OrderService {

    private final MemberRepository memberRepository = new MemoryMemberRepository();
    private final DiscountPolicy discountPolicy = new FixDiscountPolicy();

    @Override
    public Order createOrder(Long memberId, String itemName, int itemPrice) {
        Member member = memberRepository.findById(memberId);
        int discountPrice = discountPolicy.discount(member, itemPrice); // 단일 책임 원칙 잘 지킴 : OrderServiceImpl은 할인 내용 모름
        
        return new Order(memberId, itemName, itemPrice, discountPrice);
    }

}

메모리 회원 리포지토리, 고정 금액 할인 정책을 구현체로 생성
주문 생성 요청이 오면, 회원 정보를 조회하고, 할인 정책을 적용한 다음 주문 객체를 생성해서 반환


참고링크 : https://www.inflearn.com/course/%EC%8A%A4%ED%94%84%EB%A7%81-%ED%95%B5%EC%8B%AC-%EC%9B%90%EB%A6%AC-%EA%B8%B0%EB%B3%B8%ED%8E%B8?cid=325969

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