Added: ExecutorService and CompletableFuture examples

nilandev · nilandev · commit 292f322dedb0 · 2024-10-01T19:00:14.000+01:00
diff --git a/src/com/stacktips/threads/WebScraper.java b/src/com/stacktips/threads/WebScraper.java
@@ -0,0 +1,19 @@
+package com.stacktips.threads;
+
+import java.io.IOException;
+import java.net.URL;
+
+public class WebScraper {
+
+    String scrapeWebsite(String urlString) {
+        try {
+            URL url = new URL(urlString);
+            try (var stream = url.openStream()) {
+                int contentLength = stream.readAllBytes().length;
+                return String.format("URL: %s, Content Length: %d bytes", urlString, contentLength);
+            }
+        } catch (IOException e) {
+            return "Error scraping " + urlString + ": " + e.getMessage();
+        }
+    }
+}
diff --git a/src/com/stacktips/threads/WebScraperUsingCompletableFuture.java b/src/com/stacktips/threads/WebScraperUsingCompletableFuture.java
@@ -0,0 +1,58 @@
+package com.stacktips.threads;
+
+import java.util.List;
+import java.util.concurrent.*;
+
+public class WebScraperUsingCompletableFuture {
+
+    private final ExecutorService executorService;
+    private final WebScraper webScraper;
+
+    public WebScraperUsingCompletableFuture(int nThreads) {
+        this.executorService = Executors.newFixedThreadPool(nThreads);
+        this.webScraper = new WebScraper();
+    }
+
+    public List<String> scrapeWebsites(List<String> urls) {
+        List<CompletableFuture<String>> futures = urls.stream()
+            .map(url -> CompletableFuture.supplyAsync(() -> webScraper.scrapeWebsite(url), executorService)
+                .orTimeout(30, TimeUnit.SECONDS)
+                .exceptionally(e -> "Error: " + e.getMessage()))
+            .toList();
+
+        return futures.stream()
+            .map(CompletableFuture::join)
+            .toList();
+    }
+
+
+
+    public void shutdown() {
+        executorService.shutdown();
+        try {
+            if (!executorService.awaitTermination(60, TimeUnit.SECONDS)) {
+                executorService.shutdownNow();
+            }
+        } catch (InterruptedException e) {
+            executorService.shutdownNow();
+        }
+    }
+
+    public static void main(String[] args) {
+        List<String> urls = List.of(
+            "https://www.example.com",
+            "https://www.github.com",
+            "https://www.stackoverflow.com",
+            "https://www.java.com",
+            "https://www.spring.io"
+        );
+
+        WebScraperUsingCompletableFuture scraper = new WebScraperUsingCompletableFuture(3);
+        try {
+            List<String> results = scraper.scrapeWebsites(urls);
+            results.forEach(System.out::println);
+        } finally {
+            scraper.shutdown();
+        }
+    }
+}
diff --git a/src/com/stacktips/threads/WebScraperUsingExecutorService.java b/src/com/stacktips/threads/WebScraperUsingExecutorService.java
@@ -0,0 +1,65 @@
+package com.stacktips.threads;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.*;
+
+public class WebScraperUsingExecutorService {
+
+    private final ExecutorService executorService;
+    private final WebScraper webScraper;
+
+    public WebScraperUsingExecutorService(int nThreads) {
+        this.executorService = Executors.newFixedThreadPool(nThreads);
+        this.webScraper = new WebScraper();
+    }
+
+    public List<String> scrapeWebsites(List<String> urls) throws InterruptedException {
+        List<Future<String>> futures = new ArrayList<>();
+        for (String url : urls) {
+            futures.add(executorService.submit(() -> webScraper.scrapeWebsite(url)));
+        }
+
+        List<String> results = new ArrayList<>();
+        for (Future<String> future : futures) {
+            try {
+                results.add(future.get(30, TimeUnit.SECONDS));
+            } catch (ExecutionException | TimeoutException e) {
+                results.add("Error: " + e.getMessage());
+            }
+        }
+
+        return results;
+    }
+
+    public void shutdown() {
+        executorService.shutdown();
+        try {
+            if (!executorService.awaitTermination(60, TimeUnit.SECONDS)) {
+                executorService.shutdownNow();
+            }
+        } catch (InterruptedException e) {
+            executorService.shutdownNow();
+        }
+    }
+
+    public static void main(String[] args) {
+        List<String> urls = List.of(
+            "https://www.example.com",
+            "https://www.github.com",
+            "https://www.stackoverflow.com",
+            "https://www.java.com",
+            "https://www.spring.io"
+        );
+
+        WebScraperUsingExecutorService scraper = new WebScraperUsingExecutorService(3);
+        try {
+            List<String> results = scraper.scrapeWebsites(urls);
+            results.forEach(System.out::println);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        } finally {
+            scraper.shutdown();
+        }
+    }
+}
