java - 如何摆脱不必要的(？)代码——适应 DRY 原则

Question

前段时间我也在讨论类似的话题。我正在查看我的应用程序，我认为它有很多不必要的代码。我的意思是我有服务负责从两家书店的不同类别的书籍中抓取数据。现在我有 5 个类别，所以我有 5 个方法，但如果我要添加一些新类别怎么办？我将不得不添加更多方法......我认为这不是一个好的选择。现在它看起来像这样:

Controller

@GetMapping("/romances")
    public Map<Bookstore, List<Book>> get15RomanticBooks() {
        return categorizedBookService.get15BooksFromRomanceCategory();
    }

    @GetMapping("/biographies")
    public Map<Bookstore, List<Book>> get15BiographiesBooks() {
        return categorizedBookService.get15BooksFromBiographiesCategory();
    }

    @GetMapping("/guides")
    public Map<Bookstore, List<Book>> get15GuidesBooks() {
        return categorizedBookService.get15BooksFromGuidesCategory();
    }

    @GetMapping("/fantasy")
    public Map<Bookstore, List<Book>> get15FantasyBooks() {
        return categorizedBookService.get15BooksFromFantasyCategory();
    }

我在想

@GetMapping("/{category}")
public Map<......> get 15BooksFromCategory(@PathVariable CategoryType category)
{...}

我认为这是最好的方式，但服务更难。

它的服务看起来像这样:

package bookstore.scraper.book.scrapingtypeservice;

import bookstore.scraper.enums.Bookstore;
import bookstore.scraper.book.Book;
import bookstore.scraper.fetcher.empik.EmpikFetchingBookService;
import bookstore.scraper.fetcher.merlin.MerlinFetchingBookService;
import bookstore.scraper.urlproperties.EmpikUrlProperties;
import bookstore.scraper.urlproperties.MerlinUrlProperties;
import bookstore.scraper.utilities.JSoupConnector;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.EnumMap;
import java.util.List;
import java.util.Map;

@Service
@Slf4j
public class CategorizedBookService {

    private final EmpikFetchingBookService empikBookService;
    private final MerlinFetchingBookService merlinFetchingBookService;
    private final EmpikUrlProperties empikUrlProperties;
    private final MerlinUrlProperties merlinUrlProperties;
    private final JSoupConnector jSoupConnector;

    @Autowired
    public CategorizedBookService(EmpikFetchingBookService empikBookService, MerlinFetchingBookService merlinFetchingBookService, EmpikUrlProperties empikUrlProperties, MerlinUrlProperties merlinUrlProperties, JSoupConnector jSoupConnector) {
        this.empikBookService = empikBookService;
        this.merlinFetchingBookService = merlinFetchingBookService;
        this.empikUrlProperties = empikUrlProperties;
        this.merlinUrlProperties = merlinUrlProperties;
        this.jSoupConnector = jSoupConnector;
    }

    public Map<Bookstore, List<Book>> get15BooksFromRomanceCategory() {
        return get15BooksFrom(empikUrlProperties.getEmpik().getRomances(), merlinUrlProperties.getMerlin().getRomances());
    }

    public Map<Bookstore, List<Book>> get15BooksFromFantasyCategory() {
        return get15BooksFrom(empikUrlProperties.getEmpik().getFantasy(), merlinUrlProperties.getMerlin().getFantasy());
    }

    public Map<Bookstore, List<Book>> get15BooksFromCrimeCategory() {
        return get15BooksFrom(empikUrlProperties.getEmpik().getCrime(), merlinUrlProperties.getMerlin().getCrime());
    }

    public Map<Bookstore, List<Book>> get15BooksFromGuidesCategory() {
        return get15BooksFrom(empikUrlProperties.getEmpik().getGuides(), merlinUrlProperties.getMerlin().getGuides());
    }

    public Map<Bookstore, List<Book>> get15BooksFromBiographiesCategory() {
        return get15BooksFrom(empikUrlProperties.getEmpik().getBiographies(), merlinUrlProperties.getMerlin().getBiographies());
    }

    private Map<Bookstore, List<Book>> get15BooksFrom(String bookStoreEmpikURL, String bookStoreMerlinURL) {
        Map<Bookstore, List<Book>> bookstoreWith15CategorizedBooks = new EnumMap<>(Bookstore.class);

        bookstoreWith15CategorizedBooks.put(Bookstore.EMPIK, empikBookService
                .get15BooksFromCategory(jSoupConnector.connect(bookStoreEmpikURL)));
        bookstoreWith15CategorizedBooks.put(Bookstore.MERLIN, merlinFetchingBookService
                .get15BooksFromCategory(jSoupConnector.connect(bookStoreMerlinURL)));

        return bookstoreWith15CategorizedBooks;
    }
}

我必须传递 2 个不同的链接，具体取决于调用的类别。有什么办法吗？

EmpikBookService/merlinFetchingBookService 是使用 Jsoup 来抓取数据的服务。

package bookstore.scraper.fetcher.empik;

import bookstore.scraper.book.Book;
import bookstore.scraper.urlproperties.EmpikUrlProperties;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.IntStream;

@Service
public class EmpikFetchingBookService {

    private static final int FIRST_PART_PRICE = 0;
    private static final int SECOND_PART_PRICE = 1;

    private static final int BESTSELLERS_NUMBER_TO_FETCH = 5;
    private static final int CATEGORIZED_BOOKS_NUMBER_TO_FETCH = 15;
    private static final String DIV_PRODUCT_WRAPPER = "div.productWrapper";
    private static final String DATA_PRODUCT_ID = "data-product-id";

    private final EmpikUrlProperties empikUrlProperties;

    @Autowired
    public EmpikFetchingBookService(EmpikUrlProperties empikUrlProperties) {
        this.empikUrlProperties = empikUrlProperties;
    }

    public Book getMostPreciseEmpikBook(Document document) {
        String author = document.select("div.smartAuthorWrapper.ta-product-smartauthor").select("a").first().text();
        String price = convertEmpikPriceWithPossibleDiscountToActualPrice(document.select("div.price.ta-price-tile").first().text());
        String title = document.select(DIV_PRODUCT_WRAPPER).select("strong").first().text();
        String productID = document.select(DIV_PRODUCT_WRAPPER).select("a").first().attr(DATA_PRODUCT_ID);
        String bookUrl = createBookURL(title, productID);

        return Book.builder()
                .author(author)
                .price(price)
                .title(title)
                .productID(productID)
                .bookURL(bookUrl).build();
    }

    public List<Book> get5BestSellersEmpik(Document document) {
        List<Element> siteElements = document.select(DIV_PRODUCT_WRAPPER);
        List<Book> empikBestSellers = new ArrayList<>();

        IntStream.range(0, BESTSELLERS_NUMBER_TO_FETCH)
                .forEach(iteratedElement -> {

                    String author = siteElements.get(iteratedElement).select("div.smartAuthorWrapper.ta-product-smartauthor").select("a").first().text();
                    String price = convertEmpikPriceWithPossibleDiscountToActualPrice(siteElements.get(iteratedElement).select("div.price.ta-price-tile").first().text());
                    String title = siteElements.get(iteratedElement).select("strong").first().ownText();
                    String productID = siteElements.get(iteratedElement).select(DIV_PRODUCT_WRAPPER).select("a").first().attr(DATA_PRODUCT_ID);
                    String bookUrl = createBookURL(title, productID);

                    empikBestSellers.add(Book.builder()
                            .author(author)
                            .price(price)
                            .title(title)
                            .productID(productID)
                            .bookURL(bookUrl)
                            .build());
                });
        return empikBestSellers;
    }

    public List<Book> get15BooksFromCategory(Document document) {
        List<Book> books = new ArrayList<>();
        List<Element> siteElements = document.select("div.productBox__info");

        IntStream.range(0, CATEGORIZED_BOOKS_NUMBER_TO_FETCH)
                .forEach(iteratedElement -> {

                    String author = executeFetchingAuthorProcess(siteElements, iteratedElement);
                    String price = convertEmpikPriceWithPossibleDiscountToActualPrice(siteElements.get(iteratedElement).select("div.productBox__price").first().text());
                    String title = siteElements.get(iteratedElement).select("span").first().ownText();
                    String productID = siteElements.get(iteratedElement).select("a").first().attr(DATA_PRODUCT_ID);
                    String bookUrl = createBookURL(title, productID);

                    books.add(Book.builder()
                            .author(author)
                            .price(price)
                            .title(title)
                            .productID(productID)
                            .bookURL(bookUrl)
                            .build());
                });

        return books;
    }

    private String convertEmpikPriceWithPossibleDiscountToActualPrice(String price) {
        String[] splittedElements = price.split("\\s+");
        return splittedElements[FIRST_PART_PRICE] + splittedElements[SECOND_PART_PRICE];
    }

    private String createBookURL(String title, String productID) {
        return String.format(empikUrlProperties.getEmpik().getConcreteBook(), title, productID);
    }

    //method is required as on empik site, sometimes occurs null for author and we need to change code for fetching
    private static String executeFetchingAuthorProcess(List<Element> siteElements, int i) {
        String author;
        Element authorElements = siteElements.get(i).select("span > a").first();
        if (authorElements != null)
            author = authorElements.ownText();
        else
            author = siteElements.get(i).select("> span > span").first().text();
        return author;
    }
}

Answer 1

(1) 姓名get15BooksFromCategory(CategoryType)不对:您正在将要返回的一些书籍硬编码到方法名称中。

今天返15，明天返20，周日可能返5，安德鲁斯可能返50，你懂的。

考虑这些签名。

getAllBooksFromCategory(CategoryType);
getNBooksFromCategory(CategoryType, Integer);

(2) 去掉服务中的这些字段。

private final EmpikUrlProperties empikUrlProperties;
private final MerlinUrlProperties merlinUrlProperties;
private final JSoupConnector jSoupConnector;

前两个是 EmpikFetchingBookService 的一部分和 MerlinFetchingBookService ， 分别。 JSoupConnector是一个更底层的抽象，它不应该出现在这个级别。它可能驻留在这些图书服务的共同父项中，或者是一个单独的 JSoupService。共同 parent 所依赖的。

(3) 理想情况下，您应该以一个非常简单的服务结束，该服务具有单一职责 - 从其来源收集书籍。

 class BookService {
      private List<BookServiceSource> sources;

      public Map<String, List<Book>> getBooksByCategory(Category category) {
          return sources.stream()
              .collect(Collectors.toMap(BookServiceSource::getName, 
                  source -> source.getBooksByCategory(category)));
      }
 }

BookServiceSource具有与 BookService 相似的界面做。然而，MerlinSource , 作为 BookServiceSource 的子类，不会将工作委托(delegate)给其他人。相反，它会准备一个 URL 并将其提供给 JSoupService .

一个BookServiceSource的责任准备请求参数并对JSoupService返回的结果进行转换进入List<Book> .由于每个书店都有不同的 DOM，您需要知道如何将特定的 DOM 映射到您的结构中。

interface BookServiceSource {
    String getName();
    List<Book> getBooksByCategory(Category category);
}

class MerlinSource implements BookServiceSource {
    private JSoupService service;
    private MerlinUrlProperties properties;

    @Override
    public String getName() {
      return "merlin";
    }

    @Override
    public List<Book> getBooksByCategory(Category category) {
      // at this point, we have both 
      // JSoupService (to make a real request) and 
      // MerlinUrlProperties (to prepare everything for that request)
    }
}

想想 MerlinUrlProperties作为一个实用程序，可以在类别和该类别的书籍的 URL 之间提供映射。

MerlinUrlProperties可能是 Map如果它只包含一堆返回 URL 的方法，那么它本身就是一个。关键是您不必为新类别定义新方法并强制使用您的 API 的每个人都改变自己以包含 API 的新部分。用Map或者枚举，接口(interface)会更稳定。

Map<String, String> categoryToMarlinURL = new HashMap<>();

categoryToMarlinURL.put("horror", "marlin.com/horror");
categoryToMarlinURL.put("drama", "marlin.com/drama");

你拥有你需要的一切:

• 类别 ( category ),
• 该类别的 URL ( categoryToMarlinURL.get(category) ),
• 发出请求的服务 ( jSoupService.connect(categoryToMarlinURL.get(category)) )。