BAEL-6721 Add example code for notification of a complete task

core-java-modules/core-java-concurrency-simple/src/main/java/com/baeldung/concurrent/notificationForCompleteTask/AlertingFutureTask.java

@@ -0,0 +1,18 @@
+package com.baeldung.concurrent.notificationForCompleteTask;
+
+import java.util.concurrent.FutureTask;
+
+public class AlertingFutureTask extends FutureTask<String> {
+
+    private final CallbackInterface callback;
+
+    public AlertingFutureTask(Runnable runnable, Callback callback) {
+        super(runnable, null);
+        this.callback = callback;
+    }
+
+    @Override
+    protected void done() {
+        callback.taskDone("task details here");
+    }
+}

core-java-modules/core-java-concurrency-simple/src/main/java/com/baeldung/concurrent/notificationForCompleteTask/AlertingThreadPoolExecutor.java

@@ -0,0 +1,21 @@
+package com.baeldung.concurrent.notificationForCompleteTask;
+
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+
+public class AlertingThreadPoolExecutor extends ThreadPoolExecutor {
+
+    private final CallbackInterface callback;
+
+    public AlertingThreadPoolExecutor(CallbackInterface callback) {
+        super(1, 1, 60, TimeUnit.SECONDS, new ArrayBlockingQueue<>(10));
+        this.callback = callback;
+    }
+
+    @Override
+    protected void afterExecute(Runnable r, Throwable t) {
+        super.afterExecute(r, t);
+        callback.taskDone("runnable details here");
+    }
+}

core-java-modules/core-java-concurrency-simple/src/main/java/com/baeldung/concurrent/notificationForCompleteTask/Callback.java

@@ -0,0 +1,10 @@
+package com.baeldung.concurrent.notificationForCompleteTask;
+
+public class Callback implements CallbackInterface {
+
+    public void taskDone(String details){
+        System.out.println("task complete: " + details);
+        // Alerts/notifications go here
+    }
+
+}

core-java-modules/core-java-concurrency-simple/src/main/java/com/baeldung/concurrent/notificationForCompleteTask/CallbackInterface.java

@@ -0,0 +1,5 @@
+package com.baeldung.concurrent.notificationForCompleteTask;
+
+public interface CallbackInterface {
+    void taskDone(String details);
+}

core-java-modules/core-java-concurrency-simple/src/main/java/com/baeldung/concurrent/notificationForCompleteTask/RunnableImpl.java

@@ -0,0 +1,22 @@
+package com.baeldung.concurrent.notificationForCompleteTask;
+
+public class RunnableImpl implements Runnable {
+
+    private final Runnable task;
+
+    private final CallbackInterface callback;
+
+    private final String taskDoneMessage;
+
+    public RunnableImpl(Runnable task, CallbackInterface callback, String taskDoneMessage) {
+        this.task = task;
+        this.callback = callback;
+        this.taskDoneMessage = taskDoneMessage;
+    }
+
+    public void run() {
+        task.run();
+        callback.taskDone(taskDoneMessage);
+    }
+
+}

core-java-modules/core-java-concurrency-simple/src/main/java/com/baeldung/concurrent/notificationForCompleteTask/Task.java

@@ -0,0 +1,9 @@
+package com.baeldung.concurrent.notificationForCompleteTask;
+
+public class Task implements Runnable{
+    @Override
+    public void run() {
+        System.out.println("Task in progress");
+        // Business logic goes here
+    }
+}

core-java-modules/core-java-concurrency-simple/src/test/java/com/baeldung/concurrent/notificationForCompleteTask/NotificationsForCompleteTasksUnitTest.java

@@ -0,0 +1,45 @@
+package com.baeldung.concurrent.notificationForCompleteTask;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.FutureTask;
+
+import org.junit.Test;
+
+public class NotificationsForCompleteTasksUnitTest {
+
+    @Test
+    public void whenImplementingRunnable_thenReceiveNotificationOfCompletedTask() {
+        Task task = new Task();
+        Callback callback = new Callback();
+        RunnableImpl runnableImpl = new RunnableImpl(task, callback, "ready for next task");
+        runnableImpl.run();
+    }
+
+    @Test
+    public void whenUsingCompletableFuture_thenReceiveNotificationOfCompletedTask() {
+        Task task = new Task();
+        Callback callback = new Callback();
+        CompletableFuture.runAsync(task)
+          .thenAccept(result -> callback.taskDone("completion details: " + result));
+    }
+
+    @Test
+    public void whenUsingThreadPoolExecutor_thenReceiveNotificationOfCompletedTask(){
+        Task task = new Task();
+        Callback callback = new Callback();
+        AlertingThreadPoolExecutor executor = new AlertingThreadPoolExecutor(callback);
+        executor.submit(task);
+    }
+
+    @Test
+    public void whenUsingFutureTask_thenReceiveNotificationOfCompletedTask(){
+        Task task = new Task();
+        Callback callback = new Callback();
+        FutureTask<String> future = new AlertingFutureTask(task, callback);
+        ExecutorService executor = Executors.newSingleThreadExecutor();
+        executor.submit(future);
+    }
+
+}