concurrency

src/main/java/internal/hw/crawler/strategies/crawl/CrawlUtils.java

@@ -10,34 +10,47 @@ import java.net.URI;
 import java.net.URL;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Objects;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.function.BiFunction;
 import java.util.regex.Pattern;
+import java.util.stream.Collectors;
 
 public class CrawlUtils {
     private static final Logger log = LoggerFactory.getLogger(CrawlUtils.class);
+    private static final int THREAD_POOL_SIZE = 4;
 
     public static List<Article> parseHomepage(Document doc, Pattern idRegex,
                                               BiFunction<URL, Document, Article> singleParser) {
         HttpCrawler crawler = new HttpCrawler();
-        List<Article> articles = new ArrayList<>();
+        ExecutorService executor = Executors.newFixedThreadPool(THREAD_POOL_SIZE);
+        List<CompletableFuture<Article>> futures = new ArrayList<>();
+
         for (Element link : doc.getElementsByTag("a")) {
             String href = link.absUrl("href");
             if (href.isEmpty()) continue;
             if (!idRegex.matcher(href).find()) continue;
+
+            futures.add(CompletableFuture.supplyAsync(() -> {
                 try {
-                crawler.rateLimit();
                     URL articleUrl = URI.create(href).toURL();
                     Document articleDoc = crawler.fetch(articleUrl);
-                Article article = singleParser.apply(articleUrl, articleDoc);
-                if (article != null) {
-                    articles.add(article);
-                }
-            } catch (CrawlException e) {
-                log.warn("Failed to parse article: {}", href, e);
+                    return singleParser.apply(articleUrl, articleDoc);
                 } catch (Exception e) {
                     log.warn("Failed to fetch article: {}", href, e);
+                    return null;
                 }
+            }, executor));
         }
-        return articles;
+
+        executor.shutdown();
+        CompletableFuture.allOf(futures.toArray(new CompletableFuture[0])).join();
+
+        return futures.stream()
+                .map(CompletableFuture::join)
+                .filter(Objects::nonNull)
+                .collect(Collectors.toList());
     }
 }