Work on #74, updated javadocs, reformatted code to google style guide, added missing final modifiers

reactor/src/main/java/com/iluwatar/reactor/app/App.java

@@ -10,19 +10,17 @@ import com.iluwatar.reactor.framework.NioServerSocketChannel;
 import com.iluwatar.reactor.framework.ThreadPoolDispatcher;
 
 /**
- * This application demonstrates Reactor pattern. The example demonstrated is a Distributed Logging Service
+ * This application demonstrates Reactor pattern. The example demonstrated is a Distributed Logging
- * where it listens on multiple TCP or UDP sockets for incoming log requests.
+ * Service where it listens on multiple TCP or UDP sockets for incoming log requests.
  * 
  * <p>
- * <i>INTENT</i>
+ * <i>INTENT</i> <br/>
- * <br/>
  * The Reactor design pattern handles service requests that are delivered concurrently to an
  * application by one or more clients. The application can register specific handlers for processing
  * which are called by reactor on specific events.
  * 
  * <p>
- * <i>PROBLEM</i>
+ * <i>PROBLEM</i> <br/>
- * <br/>
  * Server applications in a distributed system must handle multiple clients that send them service
  * requests. Following forces need to be resolved:
  * <ul>
@@ -33,8 +31,28 @@ import com.iluwatar.reactor.framework.ThreadPoolDispatcher;
  * </ul>
  * 
  * <p>
- * The application utilizes single thread to listen for requests on all ports. It does not create
+ * <i>PARTICIPANTS</i> <br/>
- * a separate thread for each client, which provides better scalability under load (number of clients
+ * <ul>
+ * <li>Synchronous Event De-multiplexer</li> {@link NioReactor} plays the role of synchronous event
+ * de-multiplexer. It waits for events on multiple channels registered to it in an event loop.
+ * 
+ * <p>
+ * <li>Initiation Dispatcher</li> {@link NioReactor} plays this role as the application specific
+ * {@link ChannelHandler}s are registered to the reactor.
+ * 
+ * <p>
+ * <li>Handle</li> {@link AbstractNioChannel} acts as a handle that is registered to the reactor.
+ * When any events occur on a handle, reactor calls the appropriate handler.
+ * 
+ * <p>
+ * <li>Event Handler</li> {@link ChannelHandler} acts as an event handler, which is bound to a
+ * channel and is called back when any event occurs on any of its associated handles. Application
+ * logic resides in event handlers.
+ * </ul>
+ * 
+ * <p>
+ * The application utilizes single thread to listen for requests on all ports. It does not create a
+ * separate thread for each client, which provides better scalability under load (number of clients
  * increase).
  * 
  * <p>
@@ -49,6 +67,7 @@ public class App {
 
   /**
    * App entry.
+   * 
    * @throws IOException
    */
   public static void main(String[] args) throws IOException {
@@ -57,6 +76,7 @@ public class App {
 
   /**
    * Starts the NIO reactor.
+   * 
    * @throws IOException if any channel fails to bind.
    */
   public void start() throws IOException {
@@ -66,26 +86,25 @@ public class App {
     reactor = new NioReactor(new ThreadPoolDispatcher(2));
 
     /*
-		 *  This represents application specific business logic that dispatcher will call
+     * This represents application specific business logic that dispatcher will call on appropriate
-		 *  on appropriate events. These events are read events in our example.
+     * events. These events are read events in our example.
      */
     LoggingHandler loggingHandler = new LoggingHandler();
 
     /*
-		 * Our application binds to multiple channels and uses same logging handler to handle
+     * Our application binds to multiple channels and uses same logging handler to handle incoming
-		 * incoming log requests.
+     * log requests.
      */
-		reactor
+    reactor.registerChannel(tcpChannel(6666, loggingHandler)).registerChannel(tcpChannel(6667, loggingHandler))
-			.registerChannel(tcpChannel(6666, loggingHandler))
+        .registerChannel(udpChannel(6668, loggingHandler)).start();
-			.registerChannel(tcpChannel(6667, loggingHandler))
-			.registerChannel(udpChannel(6668, loggingHandler))
-		.start();
   }
 
   /**
    * Stops the NIO reactor. This is a blocking call.
+   * 
+   * @throws InterruptedException if interrupted while stopping the reactor.
    */
-	public void stop() {
+  public void stop() throws InterruptedException {
     reactor.stop();
   }
 

reactor/src/main/java/com/iluwatar/reactor/app/AppClient.java

@@ -21,10 +21,11 @@ import java.util.concurrent.TimeUnit;
  * @author npathai
  */
 public class AppClient {
-	private ExecutorService service = Executors.newFixedThreadPool(4);
+  private final ExecutorService service = Executors.newFixedThreadPool(4);
 
   /**
    * App client entry.
+   * 
    * @throws IOException if any I/O error occurs.
    */
   public static void main(String[] args) throws IOException {
@@ -34,6 +35,7 @@ public class AppClient {
 
   /**
    * Starts the logging clients.
+   * 
    * @throws IOException if any I/O error occurs.
    */
   public void start() throws IOException {
@@ -71,8 +73,8 @@ public class AppClient {
    */
   static class TCPLoggingClient implements Runnable {
 
-		private int serverPort;
+    private final int serverPort;
-		private String clientName;
+    private final String clientName;
 
     /**
      * Creates a new TCP logging client.
@@ -119,8 +121,8 @@ public class AppClient {
    * A logging client that sends requests to Reactor on UDP socket.
    */
   static class UDPLoggingClient implements Runnable {
-		private String clientName;
+    private final String clientName;
-		private InetSocketAddress remoteAddress;
+    private final InetSocketAddress remoteAddress;
 
     /**
      * Creates a new UDP logging client.
@@ -140,8 +142,7 @@ public class AppClient {
         for (int i = 0; i < 4; i++) {
 
           String message = clientName + " - Log request: " + i;
-					DatagramPacket request = new DatagramPacket(message.getBytes(),
+          DatagramPacket request = new DatagramPacket(message.getBytes(), message.getBytes().length, remoteAddress);
-							message.getBytes().length, remoteAddress);
 
           socket.send(request);
 

reactor/src/main/java/com/iluwatar/reactor/app/LoggingHandler.java

@@ -8,8 +8,8 @@ import com.iluwatar.reactor.framework.ChannelHandler;
 import com.iluwatar.reactor.framework.NioDatagramChannel.DatagramPacket;
 
 /**
- * Logging server application logic. It logs the incoming requests on standard console and returns
+ * Logging server application logic. It logs the incoming requests on standard console and returns a
- * a canned acknowledgement back to the remote peer.
+ * canned acknowledgement back to the remote peer.
  * 
  * @author npathai
  */
@@ -23,14 +23,14 @@ public class LoggingHandler implements ChannelHandler {
   @Override
   public void handleChannelRead(AbstractNioChannel channel, Object readObject, SelectionKey key) {
     /*
-		 * As this handler is attached with both TCP and UDP channels we need to check whether
+     * As this handler is attached with both TCP and UDP channels we need to check whether the data
-		 * the data received is a ByteBuffer (from TCP channel) or a DatagramPacket (from UDP channel).  
+     * received is a ByteBuffer (from TCP channel) or a DatagramPacket (from UDP channel).
      */
     if (readObject instanceof ByteBuffer) {
-			doLogging(((ByteBuffer)readObject));
+      doLogging(((ByteBuffer) readObject));
       sendReply(channel, key);
     } else if (readObject instanceof DatagramPacket) {
-			DatagramPacket datagram = (DatagramPacket)readObject;
+      DatagramPacket datagram = (DatagramPacket) readObject;
       doLogging(datagram.getData());
       sendReply(channel, datagram, key);
     } else {
@@ -40,7 +40,8 @@ public class LoggingHandler implements ChannelHandler {
 
   private void sendReply(AbstractNioChannel channel, DatagramPacket incomingPacket, SelectionKey key) {
     /*
-		 * Create a reply acknowledgement datagram packet setting the receiver to the sender of incoming message.
+     * Create a reply acknowledgement datagram packet setting the receiver to the sender of incoming
+     * message.
      */
     DatagramPacket replyPacket = new DatagramPacket(ByteBuffer.wrap(ACK));
     replyPacket.setReceiver(incomingPacket.getSender());

reactor/src/main/java/com/iluwatar/reactor/framework/AbstractNioChannel.java

@@ -10,28 +10,29 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentLinkedQueue;
 
 /**
- * This represents the <i>Handle</i> of Reactor pattern. These are resources managed by OS 
+ * This represents the <i>Handle</i> of Reactor pattern. These are resources managed by OS which can
- * which can be submitted to {@link NioReactor}. 
+ * be submitted to {@link NioReactor}.
  * 
  * <p>
- * This class serves has the responsibility of reading the data when a read event occurs and
+ * This class serves has the responsibility of reading the data when a read event occurs and writing
- * writing the data back when the channel is writable. It leaves the reading and writing of
+ * the data back when the channel is writable. It leaves the reading and writing of data on the
- * data on the concrete implementation. It provides a block writing mechanism wherein when
+ * concrete implementation. It provides a block writing mechanism wherein when any
- * any {@link ChannelHandler} wants to write data back, it queues the data in pending write queue
+ * {@link ChannelHandler} wants to write data back, it queues the data in pending write queue and
- * and clears it in block manner. This provides better throughput. 
+ * clears it in block manner. This provides better throughput.
  * 
  * @author npathai
  *
  */
 public abstract class AbstractNioChannel {
 
-	private SelectableChannel channel;
+  private final SelectableChannel channel;
-	private ChannelHandler handler;
+  private final ChannelHandler handler;
-	private Map<SelectableChannel, Queue<Object>> channelToPendingWrites = new ConcurrentHashMap<>();
+  private final Map<SelectableChannel, Queue<Object>> channelToPendingWrites = new ConcurrentHashMap<>();
   private NioReactor reactor;
 
   /**
    * Creates a new channel.
+   * 
    * @param handler which will handle events occurring on this channel.
    * @param channel a NIO channel to be wrapped.
    */
@@ -55,7 +56,8 @@ public abstract class AbstractNioChannel {
   }
 
   /**
-	 * The operation in which the channel is interested, this operation is provided to {@link Selector}.
+   * The operation in which the channel is interested, this operation is provided to
+   * {@link Selector}.
    * 
    * @return interested operation.
    * @see SelectionKey
@@ -70,8 +72,8 @@ public abstract class AbstractNioChannel {
   public abstract void bind() throws IOException;
 
   /**
-	 * Reads the data using the key and returns the read data. The underlying channel should be fetched using
+   * Reads the data using the key and returns the read data. The underlying channel should be
-	 * {@link SelectionKey#channel()}.
+   * fetched using {@link SelectionKey#channel()}.
    * 
    * @param key the key on which read event occurred.
    * @return data read.
@@ -87,8 +89,8 @@ public abstract class AbstractNioChannel {
   }
 
   /*
-	 * Called from the context of reactor thread when the key becomes writable.
+   * Called from the context of reactor thread when the key becomes writable. The channel writes the
-	 * The channel writes the whole pending block of data at once.
+   * whole pending block of data at once.
    */
   void flush(SelectionKey key) throws IOException {
     Queue<Object> pendingWrites = channelToPendingWrites.get(key.channel());
@@ -119,9 +121,9 @@ public abstract class AbstractNioChannel {
    * when this method returns. It will be written when the channel is flushed.
    * 
    * <p>
-	 * This method is used by the {@link ChannelHandler} to send reply back to the client.
+   * This method is used by the {@link ChannelHandler} to send reply back to the client. <br/>
-	 * <br/>
    * Example:
+   * 
    * <pre>
    * <code>
    * {@literal @}Override

reactor/src/main/java/com/iluwatar/reactor/framework/ChannelHandler.java

@@ -7,8 +7,8 @@ import java.nio.channels.SelectionKey;
  * to it by the {@link Dispatcher}. This is where the application logic resides.
  * 
  * <p>
- * A {@link ChannelHandler} can be associated with one or many {@link AbstractNioChannel}s, and whenever
+ * A {@link ChannelHandler} can be associated with one or many {@link AbstractNioChannel}s, and
- * an event occurs on any of the associated channels, the handler is notified of the event.
+ * whenever an event occurs on any of the associated channels, the handler is notified of the event.
  * 
  * @author npathai
  */

reactor/src/main/java/com/iluwatar/reactor/framework/Dispatcher.java

@@ -4,15 +4,15 @@ import java.nio.channels.SelectionKey;
 
 /**
  * Represents the event dispatching strategy. When {@link NioReactor} senses any event on the
- * registered {@link AbstractNioChannel}s then it de-multiplexes the event type, read or write 
+ * registered {@link AbstractNioChannel}s then it de-multiplexes the event type, read or write or
- * or connect, and then calls the {@link Dispatcher} to dispatch the read events. This decouples the I/O
+ * connect, and then calls the {@link Dispatcher} to dispatch the read events. This decouples the
- * processing from application specific processing.
+ * I/O processing from application specific processing. <br/>
- * <br/>
+ * Dispatcher should call the {@link ChannelHandler} associated with the channel on which event
- * Dispatcher should call the {@link ChannelHandler} associated with the channel on which event occurred.
+ * occurred.
  * 
  * <p>
- * The application can customize the way in which event is dispatched such as using the reactor thread to
+ * The application can customize the way in which event is dispatched such as using the reactor
- * dispatch event to channels or use a worker pool to do the non I/O processing.
+ * thread to dispatch event to channels or use a worker pool to do the non I/O processing.
  * 
  * @see SameThreadDispatcher
  * @see ThreadPoolDispatcher
@@ -21,9 +21,9 @@ import java.nio.channels.SelectionKey;
  */
 public interface Dispatcher {
   /**
-	 * This hook method is called when read event occurs on particular channel. The data read
+   * This hook method is called when read event occurs on particular channel. The data read is
-	 * is provided in <code>readObject</code>. The implementation should dispatch this read event
+   * provided in <code>readObject</code>. The implementation should dispatch this read event to the
-	 * to the associated {@link ChannelHandler} of <code>channel</code>.
+   * associated {@link ChannelHandler} of <code>channel</code>.
    * 
    * <p>
    * The type of <code>readObject</code> depends on the channel on which data was received.
@@ -36,6 +36,8 @@ public interface Dispatcher {
 
   /**
    * Stops dispatching events and cleans up any acquired resources such as threads.
+   * 
+   * @throws InterruptedException if interrupted while stopping dispatcher.
    */
-	void stop();
+  void stop() throws InterruptedException;
 }

reactor/src/main/java/com/iluwatar/reactor/framework/NioDatagramChannel.java

@@ -15,14 +15,14 @@ import java.nio.channels.SelectionKey;
  */
 public class NioDatagramChannel extends AbstractNioChannel {
 
-	private int port;
+  private final int port;
 
   /**
-	 * Creates a {@link DatagramChannel} which will bind at provided port and use <code>handler</code> to handle
+   * Creates a {@link DatagramChannel} which will bind at provided port and use <code>handler</code>
-	 * incoming events on this channel.
+   * to handle incoming events on this channel.
    * <p>
-	 * Note the constructor does not bind the socket, {@link #bind()} method should be called for binding 
+   * Note the constructor does not bind the socket, {@link #bind()} method should be called for
-	 * the socket.
+   * binding the socket.
    * 
    * @param port the port to be bound to listen for incoming datagram requests.
    * @param handler the handler to be used for handling incoming requests on this channel.
@@ -35,24 +35,25 @@ public class NioDatagramChannel extends AbstractNioChannel {
 
   @Override
   public int getInterestedOps() {
-		/* there is no need to accept connections in UDP, so the channel shows interest in 
+    /*
-		 * reading data.
+     * there is no need to accept connections in UDP, so the channel shows interest in reading data.
      */
     return SelectionKey.OP_READ;
   }
 
   /**
    * Reads and returns a {@link DatagramPacket} from the underlying channel.
+   * 
    * @return the datagram packet read having the sender address.
    */
   @Override
   public DatagramPacket read(SelectionKey key) throws IOException {
     ByteBuffer buffer = ByteBuffer.allocate(1024);
-		SocketAddress sender = ((DatagramChannel)key.channel()).receive(buffer);
+    SocketAddress sender = ((DatagramChannel) key.channel()).receive(buffer);
 
     /*
-		 * It is required to create a DatagramPacket because we need to preserve which
+     * It is required to create a DatagramPacket because we need to preserve which socket address
-		 * socket address acts as destination for sending reply packets. 
+     * acts as destination for sending reply packets.
      */
     buffer.flip();
     DatagramPacket packet = new DatagramPacket(buffer);
@@ -82,8 +83,8 @@ public class NioDatagramChannel extends AbstractNioChannel {
   }
 
   /**
-	 * Writes the pending {@link DatagramPacket} to the underlying channel sending data to 
+   * Writes the pending {@link DatagramPacket} to the underlying channel sending data to the
-	 * the intended receiver of the packet.
+   * intended receiver of the packet.
    */
   @Override
   protected void doWrite(Object pendingWrite, SelectionKey key) throws IOException {
@@ -93,7 +94,8 @@ public class NioDatagramChannel extends AbstractNioChannel {
 
   /**
    * Writes the outgoing {@link DatagramPacket} to the channel. The intended receiver of the
-	 * datagram packet must be set in the <code>data</code> using {@link DatagramPacket#setReceiver(SocketAddress)}. 
+   * datagram packet must be set in the <code>data</code> using
+   * {@link DatagramPacket#setReceiver(SocketAddress)}.
    */
   @Override
   public void write(Object data, SelectionKey key) {
@@ -126,6 +128,7 @@ public class NioDatagramChannel extends AbstractNioChannel {
 
     /**
      * Sets the sender address of this packet.
+     * 
      * @param sender the sender address.
      */
     public void setSender(SocketAddress sender) {
@@ -141,6 +144,7 @@ public class NioDatagramChannel extends AbstractNioChannel {
 
     /**
      * Sets the intended receiver address. This must be set when writing to the channel.
+     * 
      * @param receiver the receiver address.
      */
     public void setReceiver(SocketAddress receiver) {

reactor/src/main/java/com/iluwatar/reactor/framework/NioReactor.java

@@ -12,43 +12,42 @@ import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
+
 /**
  * This class acts as Synchronous Event De-multiplexer and Initiation Dispatcher of Reactor pattern.
  * Multiple handles i.e. {@link AbstractNioChannel}s can be registered to the reactor and it blocks
- * for events from all these handles. Whenever an event occurs on any of the registered handles, 
+ * for events from all these handles. Whenever an event occurs on any of the registered handles, it
- * it synchronously de-multiplexes the event which can be any of read, write or accept, and
+ * synchronously de-multiplexes the event which can be any of read, write or accept, and dispatches
- * dispatches the event to the appropriate {@link ChannelHandler} using the {@link Dispatcher}.
+ * the event to the appropriate {@link ChannelHandler} using the {@link Dispatcher}.
  * 
  * <p>
- * Implementation:
+ * Implementation: A NIO reactor runs in its own thread when it is started using {@link #start()}
- * A NIO reactor runs in its own thread when it is started using {@link #start()} method. 
+ * method. {@link NioReactor} uses {@link Selector} for realizing Synchronous Event De-multiplexing.
- * {@link NioReactor} uses {@link Selector} for realizing Synchronous Event De-multiplexing.
  * 
  * <p>
- * NOTE: This is one of the ways to implement NIO reactor and it does not take care of all possible edge cases
+ * NOTE: This is one of the ways to implement NIO reactor and it does not take care of all possible
- * which are required in a real application. This implementation is meant to demonstrate the fundamental
+ * edge cases which are required in a real application. This implementation is meant to demonstrate
- * concepts that lie behind Reactor pattern.
+ * the fundamental concepts that lie behind Reactor pattern.
  * 
  * @author npathai
  *
  */
 public class NioReactor {
 
-	private Selector selector;
+  private final Selector selector;
-	private Dispatcher dispatcher;
+  private final Dispatcher dispatcher;
   /**
    * All the work of altering the SelectionKey operations and Selector operations are performed in
    * the context of main event loop of reactor. So when any channel needs to change its readability
    * or writability, a new command is added in the command queue and then the event loop picks up
    * the command and executes it in next iteration.
    */
-	private Queue<Runnable> pendingCommands = new ConcurrentLinkedQueue<>();
+  private final Queue<Runnable> pendingCommands = new ConcurrentLinkedQueue<>();
-	private ExecutorService reactorMain = Executors.newSingleThreadExecutor();
+  private final ExecutorService reactorMain = Executors.newSingleThreadExecutor();
 
   /**
-	 * Creates a reactor which will use provided {@code dispatcher} to dispatch events.
+   * Creates a reactor which will use provided {@code dispatcher} to dispatch events. The
-	 * The application can provide various implementations of dispatcher which suits its
+   * application can provide various implementations of dispatcher which suits its needs.
-	 * needs.
    * 
    * @param dispatcher a non-null dispatcher used to dispatch events on registered channels.
    * @throws IOException if any I/O error occurs.
@@ -76,22 +75,21 @@ public class NioReactor {
 
   /**
    * Stops the reactor and related resources such as dispatcher.
+   * 
+   * @throws InterruptedException if interrupted while stopping the reactor.
    */
-	public void stop() {
+  public void stop() throws InterruptedException {
     reactorMain.shutdownNow();
     selector.wakeup();
-		try {
     reactorMain.awaitTermination(4, TimeUnit.SECONDS);
-		} catch (InterruptedException e) {
-			e.printStackTrace();
-		}
     dispatcher.stop();
   }
 
   /**
-	 * Registers a new channel (handle) with this reactor. Reactor will start waiting for events on this channel
+   * Registers a new channel (handle) with this reactor. Reactor will start waiting for events on
-	 * and notify of any events. While registering the channel the reactor uses {@link AbstractNioChannel#getInterestedOps()}
+   * this channel and notify of any events. While registering the channel the reactor uses
-	 * to know about the interested operation of this channel.
+   * {@link AbstractNioChannel#getInterestedOps()} to know about the interested operation of this
+   * channel.
    * 
    * @param channel a new channel on which reactor will wait for events. The channel must be bound
    *        prior to being registered.
@@ -117,9 +115,8 @@ public class NioReactor {
       processPendingCommands();
 
       /*
-			 * Synchronous event de-multiplexing happens here, this is blocking call which
+       * Synchronous event de-multiplexing happens here, this is blocking call which returns when it
-			 * returns when it is possible to initiate non-blocking operation on any of the 
+       * is possible to initiate non-blocking operation on any of the registered channels.
-			 * registered channels. 
        */
       selector.select();
 
@@ -152,8 +149,8 @@ public class NioReactor {
   }
 
   /*
-	 * Initiation dispatcher logic, it checks the type of event and notifier application
+   * Initiation dispatcher logic, it checks the type of event and notifier application specific
-	 * specific event handler to handle the event.
+   * event handler to handle the event.
    */
   private void processKey(SelectionKey key) throws IOException {
     if (key.isAcceptable()) {
@@ -173,7 +170,7 @@ public class NioReactor {
   private void onChannelReadable(SelectionKey key) {
     try {
       // reads the incoming data in context of reactor main loop. Can this be improved?
-			Object readObject = ((AbstractNioChannel)key.attachment()).read(key);
+      Object readObject = ((AbstractNioChannel) key.attachment()).read(key);
 
       dispatchReadEvent(key, readObject);
     } catch (IOException e) {
@@ -189,7 +186,7 @@ public class NioReactor {
    * Uses the application provided dispatcher to dispatch events to application handler.
    */
   private void dispatchReadEvent(SelectionKey key, Object readObject) {
-		dispatcher.onChannelReadEvent((AbstractNioChannel)key.attachment(), readObject, key);
+    dispatcher.onChannelReadEvent((AbstractNioChannel) key.attachment(), readObject, key);
   }
 
   private void onChannelAcceptable(SelectionKey key) throws IOException {
@@ -204,8 +201,8 @@ public class NioReactor {
    * Queues the change of operations request of a channel, which will change the interested
    * operations of the channel sometime in future.
    * <p>
-	 * This is a non-blocking method and does not guarantee that the operations have changed when
+   * This is a non-blocking method and does not guarantee that the operations have changed when this
-	 * this method returns.
+   * method returns.
    * 
    * @param key the key for which operations have to be changed.
    * @param interestedOps the new interest operations.

reactor/src/main/java/com/iluwatar/reactor/framework/NioServerSocketChannel.java

@@ -9,20 +9,21 @@ import java.nio.channels.ServerSocketChannel;
 import java.nio.channels.SocketChannel;
 
 /**
- * A wrapper over {@link NioServerSocketChannel} which can read and write data on a {@link SocketChannel}.
+ * A wrapper over {@link NioServerSocketChannel} which can read and write data on a
+ * {@link SocketChannel}.
  * 
  * @author npathai
  */
 public class NioServerSocketChannel extends AbstractNioChannel {
 
-	private int port;
+  private final int port;
 
   /**
    * Creates a {@link ServerSocketChannel} which will bind at provided port and use
    * <code>handler</code> to handle incoming events on this channel.
    * <p>
-	 * Note the constructor does not bind the socket, {@link #bind()} method should be called for binding 
+   * Note the constructor does not bind the socket, {@link #bind()} method should be called for
-	 * the socket.
+   * binding the socket.
    * 
    * @param port the port on which channel will be bound to accept incoming connection requests.
    * @param handler the handler that will handle incoming requests on this channel.
@@ -50,8 +51,8 @@ public class NioServerSocketChannel extends AbstractNioChannel {
 
   /**
    * Reads and returns {@link ByteBuffer} from the underlying {@link SocketChannel} represented by
-	 * the <code>key</code>. Due to the fact that there is a dedicated channel for each client connection
+   * the <code>key</code>. Due to the fact that there is a dedicated channel for each client
-	 * we don't need to store the sender.
+   * connection we don't need to store the sender.
    */
   @Override
   public ByteBuffer read(SelectionKey key) throws IOException {
@@ -72,18 +73,18 @@ public class NioServerSocketChannel extends AbstractNioChannel {
    */
   @Override
   public void bind() throws IOException {
-		((ServerSocketChannel)getChannel()).socket().bind(new InetSocketAddress(InetAddress.getLocalHost(), port));
+    ((ServerSocketChannel) getChannel()).socket().bind(new InetSocketAddress(InetAddress.getLocalHost(), port));
-		((ServerSocketChannel)getChannel()).configureBlocking(false);
+    ((ServerSocketChannel) getChannel()).configureBlocking(false);
     System.out.println("Bound TCP socket at port: " + port);
   }
 
   /**
-	 * Writes the pending {@link ByteBuffer} to the underlying channel sending data to 
+   * Writes the pending {@link ByteBuffer} to the underlying channel sending data to the intended
-	 * the intended receiver of the packet.
+   * receiver of the packet.
    */
   @Override
   protected void doWrite(Object pendingWrite, SelectionKey key) throws IOException {
     ByteBuffer pendingBuffer = (ByteBuffer) pendingWrite;
-		((SocketChannel)key.channel()).write(pendingBuffer);
+    ((SocketChannel) key.channel()).write(pendingBuffer);
   }
 }

reactor/src/main/java/com/iluwatar/reactor/framework/SameThreadDispatcher.java

@@ -4,8 +4,8 @@ import java.nio.channels.SelectionKey;
 
 /**
  * Dispatches the events in the context of caller thread. This implementation is a good fit for
- * small applications where there are limited clients. Using this implementation limits the scalability
+ * small applications where there are limited clients. Using this implementation limits the
- * because the I/O thread performs the application specific processing.
+ * scalability because the I/O thread performs the application specific processing.
  * 
  * <p>
  * For better performance use {@link ThreadPoolDispatcher}.
@@ -17,21 +17,18 @@ import java.nio.channels.SelectionKey;
 public class SameThreadDispatcher implements Dispatcher {
 
   /**
-	 * Dispatches the read event in the context of caller thread.
+   * Dispatches the read event in the context of caller thread. <br/>
-	 * <br/>
+   * Note this is a blocking call. It returns only after the associated handler has handled the read
-	 * Note this is a blocking call. It returns only after the associated handler has handled the
+   * event.
-	 * read event.
    */
   @Override
   public void onChannelReadEvent(AbstractNioChannel channel, Object readObject, SelectionKey key) {
-		if (channel.getHandler() != null) {
     /*
      * Calls the associated handler to notify the read event where application specific code
      * resides.
      */
     channel.getHandler().handleChannelRead(channel, readObject, key);
   }
-	}
 
   /**
    * No resources to free.

reactor/src/main/java/com/iluwatar/reactor/framework/ThreadPoolDispatcher.java

@@ -6,16 +6,16 @@ import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 
 /**
- * An implementation that uses a pool of worker threads to dispatch the events. This provides
+ * An implementation that uses a pool of worker threads to dispatch the events. This provides better
- * better scalability as the application specific processing is not performed in the context
+ * scalability as the application specific processing is not performed in the context of I/O
- * of I/O (reactor) thread.
+ * (reactor) thread.
  * 
  * @author npathai
  *
  */
-public class ThreadPoolDispatcher extends SameThreadDispatcher {
+public class ThreadPoolDispatcher implements Dispatcher {
 
-	private ExecutorService executorService;
+  private final ExecutorService executorService;
 
   /**
    * Creates a pooled dispatcher with tunable pool size.
@@ -27,29 +27,24 @@ public class ThreadPoolDispatcher extends SameThreadDispatcher {
   }
 
   /**
-	 * Submits the work of dispatching the read event to worker pool, where it gets picked
+   * Submits the work of dispatching the read event to worker pool, where it gets picked up by
-	 * up by worker threads. 
+   * worker threads. <br/>
-	 * <br/>
+   * Note that this is a non-blocking call and returns immediately. It is not guaranteed that the
-	 * Note that this is a non-blocking call and returns immediately. It is not guaranteed 
+   * event has been handled by associated handler.
-	 * that the event has been handled by associated handler.
    */
   @Override
   public void onChannelReadEvent(AbstractNioChannel channel, Object readObject, SelectionKey key) {
-		executorService.execute(() -> 
+    executorService.execute(() -> channel.getHandler().handleChannelRead(channel, readObject, key));
-			ThreadPoolDispatcher.super.onChannelReadEvent(channel, readObject, key));
   }
 
   /**
    * Stops the pool of workers.
+   * 
+   * @throws InterruptedException if interrupted while stopping pool of workers.
    */
   @Override
-	public void stop() {
+  public void stop() throws InterruptedException {
-		executorService.shutdownNow();
+    executorService.shutdown();
-		try {
     executorService.awaitTermination(4, TimeUnit.SECONDS);
-		} catch (InterruptedException e) {
-			e.printStackTrace();
   }
-	}
-
 }

reactor/src/test/java/com/iluwatar/reactor/app/AppTest.java

@@ -4,16 +4,30 @@ import java.io.IOException;
 
 import org.junit.Test;
 
+/**
+ * 
+ * This class tests the Distributed Logging service by starting a Reactor and then sending it
+ * concurrent logging requests using multiple clients.
+ * 
+ * @author npathai
+ */
 public class AppTest {
 
+  /**
+   * Test the application.
+   * 
+   * @throws IOException if any I/O error occurs.
+   * @throws InterruptedException if interrupted while stopping the application.
+   */
   @Test
-	public void testApp() throws IOException {
+  public void testApp() throws IOException, InterruptedException {
     App app = new App();
     app.start();
 
     AppClient client = new AppClient();
     client.start();
 
+    // allow clients to send requests. Artificial delay.
     try {
       Thread.sleep(2000);
     } catch (InterruptedException e) {