Added Guava thread pool examples (#589)

core-java-8/src/main/java/com/baeldung/threadpool/ExitingExecutorServiceExample.java

@@ -0,0 +1,29 @@
+package com.baeldung.threadpool;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+
+import com.google.common.util.concurrent.MoreExecutors;
+
+/**
+ * This class demonstrates the usage of Guava's exiting executor services that keep the VM from hanging.
+ * Without the exiting executor service, the task would hang indefinitely.
+ * This behaviour cannot be demonstrated in JUnit tests, as JUnit kills the VM after the tests.
+ */
+public class ExitingExecutorServiceExample {
+
+    public static void main(String... args) {
+
+        ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newFixedThreadPool(5);
+        ExecutorService executorService = MoreExecutors.getExitingExecutorService(executor, 100, TimeUnit.MILLISECONDS);
+
+        executorService.submit(() -> {
+            while (true) {
+            }
+        });
+
+    }
+
+}

core-java-8/src/test/java/com/baeldung/threadpool/GuavaThreadPoolTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.threadpool;
+
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.stream.Collectors;
+
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.common.util.concurrent.ListeningExecutorService;
+import com.google.common.util.concurrent.MoreExecutors;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public class GuavaThreadPoolTest {
+
+    @Test
+    public void whenExecutingTaskWithDirectExecutor_thenTheTaskIsExecutedInTheCurrentThread() {
+
+        Executor executor = MoreExecutors.directExecutor();
+
+        AtomicBoolean executed = new AtomicBoolean();
+
+        executor.execute(() -> {
+            try {
+                Thread.sleep(500);
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+            executed.set(true);
+        });
+
+        assertTrue(executed.get());
+    }
+
+    @Test
+    public void whenJoiningFuturesWithAllAsList_thenCombinedFutureCompletesAfterAllFuturesComplete() throws ExecutionException, InterruptedException {
+
+        ExecutorService executorService = Executors.newCachedThreadPool();
+        ListeningExecutorService listeningExecutorService = MoreExecutors.listeningDecorator(executorService);
+
+        ListenableFuture<String> future1 = listeningExecutorService.submit(() -> "Hello");
+        ListenableFuture<String> future2 = listeningExecutorService.submit(() -> "World");
+
+        String greeting = Futures.allAsList(future1, future2).get()
+                .stream()
+                .collect(Collectors.joining(" "));
+        assertEquals("Hello World", greeting);
+
+    }
+
+}