Fixed all the code changes after review

Author: Chandana Amarnath

queue-load-leveling/README.md

@@ -31,4 +31,4 @@ for both the task and the service.
 
 ## Credits
 
-* [Design Pattern: Queue-Based Load Leveling Pattern](https://msdn.microsoft.com/en-us/library/dn589783.aspx)
+* [Microsoft Cloud Design Patterns: Queue-Based Load Leveling Pattern](https://msdn.microsoft.com/en-us/library/dn589783.aspx)

queue-load-leveling/src/main/java/org/queue/load/leveling/App.java

@@ -23,6 +23,10 @@
 
 package org.queue.load.leveling;
 
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -58,37 +62,56 @@ public class App {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
 
+  //Executor shut down time limit.
+  private static final int SHUTDOWN_TIME = 15;
+  
   /**
    * Program entry point
    * 
    * @param args command line args
    */
   public static void main(String[] args) {
+    
+    // An Executor that provides methods to manage termination and methods that can 
+    // produce a Future for tracking progress of one or more asynchronous tasks.
+    ExecutorService executor = null;
+    
     try {
       // Create a MessageQueue object.
       MessageQueue msgQueue = new MessageQueue();
 
-      LOGGER.info("All the TaskGenerators started.");
+      LOGGER.info("Submitting TaskGenerators and ServiceExecutor threads.");
 
       // Create three TaskGenerator threads. Each of them will submit different number of jobs.
       Runnable taskRunnable1 = new TaskGenerator(msgQueue, 5);
       Runnable taskRunnable2 = new TaskGenerator(msgQueue, 1);
       Runnable taskRunnable3 = new TaskGenerator(msgQueue, 2);
 
-      Thread taskGenerator1 = new Thread(taskRunnable1, "Task_Generator_1");
-      Thread taskGenerator2 = new Thread(taskRunnable2, "Task_Generator_2");
-      Thread taskGenerator3 = new Thread(taskRunnable3, "Task_Generator_3");
+      // Create e service which should process the submitted jobs.
+      Runnable srvRunnable = new ServiceExecutor(msgQueue);
+
+      // Create a ThreadPool of 2 threads and
+      // submit all Runnable task for execution to executor..
+      executor = Executors.newFixedThreadPool(2);
+      executor.submit(taskRunnable1);
+      executor.submit(taskRunnable2);
+      executor.submit(taskRunnable3);
 
-      taskGenerator1.start();
-      taskGenerator2.start();
-      taskGenerator3.start();
+      // submitting serviceExecutor thread to the Executor service.
+      executor.submit(srvRunnable);
 
-      LOGGER.info("Service Executor started.");
+      // Initiates an orderly shutdown.
+      LOGGER.info("Intiating shutdown. Executor will shutdown only after all the Threads are completed.");
+      executor.shutdown();
 
-      // First create e service which will process all the jobs.
-      Runnable srvRunnable = new ServiceExecutor(msgQueue);
-      Thread srvExec = new Thread(srvRunnable, "Service_Executor_Thread");
-      srvExec.start();
+      // Wait for SHUTDOWN_TIME seconds for all the threads to complete 
+      // their tasks and then shut down the executor and then exit. 
+      if ( !executor.awaitTermination(SHUTDOWN_TIME, TimeUnit.SECONDS) ) {
+        LOGGER.info("Executor was shut down and Exiting.");
+        executor.shutdownNow();
+      }
+    } catch (InterruptedException ie) {
+      LOGGER.error(ie.getMessage());
     } catch (Exception e) {
       LOGGER.error(e.getMessage());
     }

queue-load-leveling/src/main/java/org/queue/load/leveling/Message.java

@@ -27,12 +27,8 @@
  *
 */
 public class Message {
-  private String msg;
-
-  // Empty constructor.
-  public Message() {
-  }
-  
+  private final String msg;
+ 
   // Parameter constructor.
   public Message(String msg) {
     super();
@@ -44,11 +40,6 @@ public String getMsg() {
     return msg;
   }
 
-  // Set Method for attribute msg.
-  public void setMsg(String msg) {
-    this.msg = msg;
-  }
-  
   @Override
   public String toString() {
     return msg;

queue-load-leveling/src/main/java/org/queue/load/leveling/MessageQueue.java

@@ -38,7 +38,7 @@ public class MessageQueue {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
 
-  private BlockingQueue<Message> blkQueue;
+  private final BlockingQueue<Message> blkQueue;
 
   // Default constructor when called creates Blocking Queue object. 
   public MessageQueue() {

queue-load-leveling/src/main/java/org/queue/load/leveling/ServiceExecutor.java

@@ -36,7 +36,7 @@ public class ServiceExecutor implements Runnable {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
 
-  private MessageQueue msgQueue;
+  private final MessageQueue msgQueue;
 
   public ServiceExecutor(MessageQueue msgQueue) {
     this.msgQueue = msgQueue;
@@ -53,12 +53,12 @@ public void run() {
         if (null != msg) {
           LOGGER.info(msg.toString() + " is served.");
         } else {
-          LOGGER.info("ServiceExecutor: All tasks are executed. Waiting.");
+          LOGGER.info("Service Executor: Waiting for Messages to serve .. ");
         }
 
         Thread.sleep(1000);
       }
-    } catch (InterruptedException ie) { 
+    } catch (InterruptedException ie) {
       LOGGER.error(ie.getMessage());
     } catch (Exception e) {
       LOGGER.error(e.getMessage());

queue-load-leveling/src/main/java/org/queue/load/leveling/TaskGenerator.java

@@ -37,10 +37,10 @@ public class TaskGenerator implements Task, Runnable {
   private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
 
   // MessageQueue reference using which we will submit our messages.
-  private MessageQueue msgQueue;
+  private final MessageQueue msgQueue;
 
   // Total message count that a TaskGenerator will submit.
-  private int msgCount;
+  private final int msgCount;
 
   // Parameterized constructor.
   public TaskGenerator(MessageQueue msgQueue, int msgCount) {
@@ -64,16 +64,18 @@ public void submit(Message msg) {
    * After every message submission TaskGenerator thread will sleep for 1 second.
    */
   public void run() {
+    
+    int count = this.msgCount;
+    
     try {
-      while (this.msgCount > 0) {
-        String statusMsg = "Message-" + this.msgCount + " submitted by " + Thread.currentThread().getName();
-        Message newMessage = new Message(statusMsg);
-        this.submit(newMessage);
+      while (count > 0) {
+        String statusMsg = "Message-" + count + " submitted by " + Thread.currentThread().getName();
+        this.submit(new Message(statusMsg));
 
         LOGGER.info(statusMsg);
 
         // reduce the message count.
-        this.msgCount--;
+        count--;
 
         // Make the current thread to sleep after every Message submission.
         Thread.sleep(1000);

queue-load-leveling/src/test/java/org/queue/load/leveling/AppTest.java

@@ -27,7 +27,7 @@
 import org.junit.Test;
 
 /**
- * Tests that Caching example runs without errors.
+ * Application Test
  */
 public class AppTest {
   @Test

queue-load-leveling/src/test/java/org/queue/load/leveling/MessageQueueTest.java

@@ -22,9 +22,10 @@
  */
 package org.queue.load.leveling;
 
-import org.junit.Test;
 import static org.junit.Assert.assertEquals;
 
+import org.junit.Test;
+
 /**
  * 
  * Test case for submitting and retrieving messages from Blocking Queue.
@@ -36,13 +37,12 @@ public class MessageQueueTest {
   public void messageQueueTest() {
 
     MessageQueue msgQueue = new MessageQueue();
-    Message msg = new Message("MessageQueue Test");
 
     // submit message
-    msgQueue.submitMsg(msg);
+    msgQueue.submitMsg(new Message("MessageQueue Test"));
 
     // retrieve message
-    assertEquals(msg.getMsg(), msgQueue.retrieveMsg().getMsg());
+    assertEquals(msgQueue.retrieveMsg().getMsg(), "MessageQueue Test");
   }
 
 }

queue-load-leveling/src/test/java/org/queue/load/leveling/MessageTest.java

@@ -39,10 +39,5 @@ public void messageTest() {
     String testMsg = "Message Test";
     Message msg = new Message(testMsg);
     assertEquals(msg.getMsg(), testMsg);
-
-    // Default constructor and setter method test.
-    Message simpleMsg = new Message();
-    simpleMsg.setMsg(testMsg);
-    assertEquals(simpleMsg.getMsg(), testMsg);
   }
 }