[REST API] 1. DTO

1. Java Project 생성

package model;


import lombok.Builder;
import lombok.Data;

// 주문 번호
@Data
public class Order {
    private int id;

    @Builder
    public Order(int id) {
        this.id = id;
    }
}

package model;

import lombok.Builder;
import lombok.Data;

// 주문 옵션(메뉴)
@Data
public class OrderOption {
    private int id;
    private String optionName; // 하얀티
    private int qty; // 5개
    private int totalPrice; // 10000원

    private Product product;
    private Order order;

    @Builder
    public OrderOption(int id, String optionName, int qty, int totalPrice, Product product, Order order) {
        this.id = id;
        this.optionName = optionName;
        this.qty = qty;
        this.totalPrice = totalPrice;
        this.product = product;
        this.order = order;
    }
}

package model;

import lombok.Builder;
import lombok.Data;

@Data
public class Product {
    private int id;
    private String name; // 바지

    @Builder
    public Product(int id, String name) {
        this.id = id;
        this.name = name;
    }
}

package model;

import lombok.Builder;
import lombok.Data;

@Data
public class ProductOption {
    private int id;
    private String name;
    private int price;
    private int qty;
    private Product product;

    @Builder
    public ProductOption(int id, String name, int price, int qty, Product product) {
        this.id = id;
        this.name = name;
        this.price = price;
        this.qty = qty;
        this.product = product;
    }
}

2. 문제 풀이

• 1 ~ 4번 문제 : 화면 출력에 알맞은 DTO 제작

package ex01;

import com.google.gson.Gson;
import model.Order;
import model.OrderOption;
import model.Product;
import model.ProductOption;

import java.util.Arrays;
import java.util.List;

public class App1 {
    public static void main(String[] args) {
        // 판매자 로직
        // 1. 상품 2개
        Product p1 = new Product(1, "바지");
        Product p2 = new Product(2, "티");
        List<Product> products = Arrays.asList(p1, p2); // 1번 문제 -> List<Product>를 List<ProductDTO>로 옮기기
        
        // 2. 상품 옵션 4개 생성
        ProductOption op1 = new ProductOption(1, "파란바지", 1000, 10, p1);
        ProductOption op2 = new ProductOption(2, "빨간바지", 2000, 10, p1);
        ProductOption op3 = new ProductOption(3, "노랑티", 1000, 10, p2);
        ProductOption op4 = new ProductOption(4, "하얀티", 2000, 10, p2);
        List<ProductOption> p1Options = Arrays.asList(op1, op2);
        List<ProductOption> p2Options = Arrays.asList(op3, op4); // 2번 문제 -> p2, p2Options -> ProductDetailDTO 로 옮기기

        // 구매자 로직
        // 3. 구매
        Order or1 = new Order(1);
        OrderOption orOption1 = new OrderOption(1, "파란바지", 2, 2000, p1, or1);
        OrderOption orOption2 = new OrderOption(2, "빨간바지", 2, 4000, p1, or1);
        OrderOption orOption3 = new OrderOption(3, "하얀티", 5, 10000, p2, or1);

        op1.setQty(op1.getQty() - 2);
        op2.setQty(op2.getQty() - 2);
        op4.setQty(op4.getQty() - 5);


        Order or2 = new Order(2);
        OrderOption orOption4 = new OrderOption(4, "노랑티", 7, 7000, p2, or2);

        op3.setQty(op3.getQty() - 7);

        // 4. 상품 출력
        // 1번 문제 : 상품 목록 화면
        // List<Product> -> List<ProductDTO>

        // 2번 문제 : 상품 상세 화면 (p2)
        // Product(p2, p2Options) -> ProductDetail


        // 3번 문제 : 주문 확인 상세 화면 (or2)
        // 틀렸음 : DTO 담기


        // 4번 문제 : 주문 확인 상세 화면 (or1)
        // (orOption1, orOption2), (orOption3) -> OrderDetailDTO

    }
}

해답

1번 문제

• Product를 저장하는 DTO : 깊은 복사

package ex01;

import lombok.Data;
import model.Product;

@Data
public class ProductDTO {
    private int id;
    private String name;

    public ProductDTO(Product product) {
        this.id = product.getId();
        this.name = product.getName();
    }
}

List<ProductDTO> productsDTO = Arrays.asList(new ProductDTO(p1), new ProductDTO(p2));

• 출력은 GSON 활용 : JSON 형태로 결과를 출력

Gson gson = new Gson();
String ex01 = gson.toJson(productsDTO);
System.out.println(ex01);

2번 문제

• 하나의 DTO 안에 여러 객체가 저장되어야 함

package ex01;

import lombok.Data;
import model.Product;
import model.ProductOption;

import java.util.ArrayList;
import java.util.List;

@Data
public class ProductDetailDTO {
    private Integer productId;
    private String productName;
    List<ProductOptionDTO> options = new ArrayList<>();

    public ProductDetailDTO(Product p, List<ProductOption> options) {
        this.productId = p.getId();
        this.productName = p.getName();
        for (ProductOption op : options) {
            this.options.add(new ProductOptionDTO(op));
        }
    }

    @Data
    public class ProductOptionDTO {
        private int optionId;
        private String optionName;
        private int optionPrice;
        private int optionQty;

        public ProductOptionDTO(ProductOption op) {
            this.optionId = op.getId();
            this.optionName = op.getName();
            this.optionPrice = op.getPrice();
            this.optionQty = op.getQty();
        }
    }
}

ProductDetailDTO productDetailDTO = new ProductDetailDTO(p2, p2Options);

String ex02 = gson.toJson(productDetailDTO);
System.out.println(ex02);

3번 문제

• Order와 Product의 구분을 확실히 해야 함

package ex01;

import lombok.Data;
import model.OrderOption;

// 3번 문제만을 위한 DTO
@Data
public class TempDTO {
    private Integer orderId;
    private Integer productId;
    private Integer orderOptionId;
    private String orderOptionName;
    private Integer orderOptionQty;
    private Integer totalPrice;

    public TempDTO(OrderOption orderOption) {
        this.orderId = orderOption.getOrder().getId();
        this.productId = orderOption.getProduct().getId(); // Lazy Loading (조인 안했다면)
        this.orderOptionId = orderOption.getId();
        this.orderOptionName = orderOption.getOptionName();
        this.orderOptionQty = orderOption.getQty();
        this.totalPrice = orderOption.getTotalPrice();
    }
}

TempDTO tempDTO = new TempDTO(orOption4);

String ex03 = gson.toJson(tempDTO);
System.out.println(ex03);

4번 문제

• DTO → DTO → DTO의 연쇄 작용

package ex01;

import lombok.Data;
import model.OrderOption;

import java.util.ArrayList;
import java.util.List;

@Data
public class OrderDetailDTO {
    private Integer orderId;
    private List<X> products;
    private Integer totalPrice = 0;

    public OrderDetailDTO(List<OrderOption> orderOptions) { // p1(orOption1, orOption2), p2(orOption3)
        System.out.println("*");
        this.orderId = orderOptions.getFirst().getOrder().getId();

        List<OrderOption> op1s = new ArrayList<>();
        op1s.add(orderOptions.get(0));
        op1s.add(orderOptions.get(1));

        List<OrderOption> op2s = new ArrayList<>();
        op2s.add(orderOptions.get(2));

        X x1 = new X(op1s);
        X x2 = new X(op2s);

        List<X> xList = new ArrayList<>();
        xList.add(x1);
        xList.add(x2);

        this.products = xList;

        for (OrderOption op : orderOptions) {
            this.totalPrice += op.getTotalPrice();
        }
    }

    @Data
    public class X {
        private Integer productId;
        private List<Y> orderOptions;

        public X(List<OrderOption> orderOptions) {
            System.out.println("**");
            this.productId = orderOptions.getFirst().getProduct().getId();
            List<Y> yList = new ArrayList<>();
            for (OrderOption orderOption : orderOptions) {
                yList.add(new Y(orderOption));
            }

            this.orderOptions = yList;
        }

        @Data
        public class Y {
            private Integer orderOptionId;
            private String orderOptionName;
            private Integer orderOptionQty;
            private Integer orderOptionTotalPrice;

            public Y(OrderOption orderOption) {
                System.out.println("***");
                this.orderOptionId = orderOption.getId();
                this.orderOptionName = orderOption.getOptionName();
                this.orderOptionQty = orderOption.getQty();
                this.orderOptionTotalPrice = orderOption.getTotalPrice();
            }
        }
    }
}

List<OrderOption> or1Options = Arrays.asList(orOption1, orOption2, orOption3);
OrderDetailDTO orderDetailDTO = new OrderDetailDTO(or1Options);

String ex04 = gson.toJson(orderDetailDTO);
System.out.println(ex04);

4번 문제 풀이 보완

1. 리스트 동적 제작

2. 멤버 동적 삽입

package ex01;

import lombok.Data;
import model.OrderOption;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

@Data
public class OrderDetailDTO {
    private int orderId;
    private List<ProductDTO> products = new ArrayList<>();
    private int sumPrice;

    public OrderDetailDTO(List<OrderOption> orderOptions) {
        this.orderId = orderOptions.getFirst().getId();

        // 중복이 제거된 상품 ids + 전체금액 계산
        Set<Integer> productIds = new HashSet<>();
        for (OrderOption orderOption : orderOptions) {
            productIds.add(orderOption.getProduct().getId());
            this.sumPrice += orderOption.getTotalPrice();
        }

        // 상품별 주문한 상품옵션 만들기
        for (Integer productId : productIds) {

            List<OrderOption> selectedOptions = new ArrayList<>();

            for (OrderOption orderOption : orderOptions) {
                if (productId == orderOption.getProduct().getId()) {
                    selectedOptions.add(orderOption);
                }
            }

            ProductDTO productDTO = new ProductDTO(productId, selectedOptions);
            this.products.add(productDTO);
        }
    }

    @Data
    class ProductDTO {
        private int productId;
        private List<OrderOptionDTO> orderOptions = new ArrayList<>();

        public ProductDTO(int productId, List<OrderOption> orderOptions) {
            this.productId = productId;

            for (OrderOption orderOption : orderOptions) {
                this.orderOptions.add(new OrderOptionDTO(orderOption));
            }
        }

        @Data
        class OrderOptionDTO {
            private int orderOptionId;
            private String orderOptionName;
            private int orderQty;
            private int orderTotalPrice;

            public OrderOptionDTO(OrderOption orderOption) {
                this.orderOptionId = orderOption.getId();
                this.orderOptionName = orderOption.getOptionName();
                this.orderQty = orderOption.getQty();
                this.orderTotalPrice = orderOption.getTotalPrice();
            }
        }
    }
}

• 결과는 동일