// Event Header// int: event type// int: client ID// int: size of your payload// Assume the use of an Event class, that has a write(ByteBuffer bb)// method used to write the Event data on itByteBuffer bb = ByteBuffer.allocate(1024);bb.putInt(evt.getType());bb.putInt(evt.getClientID());int sizePos = writeBuffer.position();bb.putInt(0); // here we set the payload size// write the event on the ByteBuffer// It must return the position of the ByteBuffer after the writting// So that we know what is header info, and what's dataint payloadSize = event.write(bb); bb.putInt(sizePos, payloadSize); // Place the size, after writting the event bb.flip(); // ready for writting (sending) to the server)

[source language="java"]/*author: gamediaceo@yahoo.comdescription: Chat class, allows user to type in input*//*dependencies*/import java.io.*;import java.util.*;//networkimport java.net.*;public class Chat implements Runnable{	//associated thread object	Thread thread;		BufferedReader reader;		DataOutputStream out;		public Chat(DataOutputStream out) throws Exception	{		this.out = out;						reader = new BufferedReader(new InputStreamReader(System.in));				thread = new Thread(this);		thread.start();	}			public void run()	{		while (true)		{			String line;						synchronized (out)			{				try				{					line = reader.readLine();										line = line + "\n";										out.writeBytes(line);				}				catch (Exception ex)				{					ex.printStackTrace();									}				}			}				}	}

[source language="Java"]/*author: gamediaceo@yahoo.comdescription: The Simple Chat Client main class. runs the main loop*//*dependencies*/import java.io.*;import java.util.*;//networkimport java.net.*;public class Client{		Socket socket;		DataOutputStream out;		DataInputStream in;		Chat chat;		//constructor	public Client(String host,int port)	{		System.out.println("Connecting to " + host + ":" + port);				try		{			socket = new Socket(host,port);						out = new DataOutputStream(socket.getOutputStream());						in = new DataInputStream(socket.getInputStream());		}		catch (UnknownHostException ex)		{			System.out.println("Unknown host");						ex.printStackTrace();						System.exit(-1);		}		catch (IOException ex)		{			System.out.println("Couldn't get I/O for " + host);						ex.printStackTrace();						System.exit(-1);		}						if (socket == null)		{			System.out.println("Socket doesn't exist!");						System.exit(-1);			}				if (out == null)		{			System.out.println("OutStream doesn't exist!");						System.exit(-1);		}				if (in == null)		{			System.out.println("InStream doesn't exist!");						System.exit(-1);		}			}		//destructor	public void finalize() throws Exception	{		out.close();				in.close();				socket.close();							}		public void run()	{		String response;				try		{			chat = new Chat(out);		}		catch (Exception ex)		{			ex.printStackTrace();		}				//every time receive a message from the server, print it		while (true)		{			try			{				response = in.readLine();								if (response != null)				{					System.out.println(response);				}			}			catch (IOException ex)			{				ex.printStackTrace();			}						}			}	}

[source language="Java"]/*author: gamediaceo@yahoo.comdescription: The Simple Chat Client main class. runs the main loop*//*dependencies*/import java.io.*;import java.util.*;public class SimpleChat{	final static int CONNECT_PORT=42040;		Client client;		public SimpleChat(String host)	{		try		{			client = new Client(host,CONNECT_PORT);		}		catch (Exception ex)		{			ex.printStackTrace();		}	}		public static void main(String args[])	{		SimpleChat simpleChat = new SimpleChat(args[0]);					simpleChat.client.run();		}			}

/*author: gamediaceo@yahoo.comdescription: The Simple Chat Server main class. the actual server loop*//*dependencies*/import java.io.*;import java.util.*;//networkimport java.net.*;import java.nio.*;import java.nio.channels.*;import java.nio.channels.spi.*;import java.nio.charset.*;public class Server implements Runnable{	Thread thread;		Selector selector;		ServerSocketChannel serverChannel;		//needed for decoding/encoding	Charset asciiCharset;		CharsetDecoder asciiDecoder;		CharsetEncoder asciiEncoder;		//constructor	//start the listener server	public Server(int listenPort) throws Exception	{		//create the selector		selector = Selector.open();				//create the server socket channel		serverChannel = ServerSocketChannel.open();				//set nonblocking		serverChannel.configureBlocking(false);				//bind		InetSocketAddress address = new InetSocketAddress(listenPort);				serverChannel.socket().bind(address);				//register		serverChannel.register(selector,SelectionKey.OP_ACCEPT);				asciiCharset = Charset.forName("US-ASCII");				asciiDecoder = asciiCharset.newDecoder();				asciiEncoder = asciiCharset.newEncoder();				thread = new Thread(this);				thread.start();	}		//destructor	public void finalize() throws Exception	{		selector.close();					}		//main	public void run()	{		//flag for loop. set to false when the server wants to exit		boolean stillRunning = true;				while (stillRunning)		{			try			{								synchronized (selector)				{					//now read					int numKeys = selector.select();										if (numKeys > 0)					{						readRequests();					}				}			}			catch (Exception ex)			{				ex.printStackTrace();			}					}	}		//read the requests	public void readRequests() throws Exception	{		Set readyKeys = selector.selectedKeys();				for (Iterator i=readyKeys.iterator(); i.hasNext(); )		{			//grab the key			SelectionKey key = (SelectionKey) i.next();						//remove the it			i.remove();						if (key.isAcceptable())			{				registerPendingConnection(key);			}						if (key.isReadable())			{				((ReadWriteCallback)key.attachment()).read();							}					}	}		//establish comm-link with client	protected void registerPendingConnection(SelectionKey key) throws Exception	{		SocketChannel channel = serverChannel.accept();				//set async		channel.configureBlocking(false);					//create a callback		ReadWriteCallback rwCallback = new ReadWriteCallback(channel,this,asciiDecoder);					//register		channel.register(selector,SelectionKey.OP_READ,rwCallback);			}		//retrieve the set of callbacks	public Set getChannelCallbacks()	{		Set channelCallbacks = new HashSet(24);	//24 is the max number of clients				Set keys = selector.keys();				synchronized (keys)		{			for (Iterator i=keys.iterator(); i.hasNext(); )			{				SelectionKey key = (SelectionKey)i.next();								if (key.interestOps() != SelectionKey.OP_ACCEPT)				{					Object attachment = key.attachment();										channelCallbacks.add(attachment);				}			}		}				return channelCallbacks;	}		}

/*author: gamediaceo@yahoo.comdescription: Called whenever*//*dependencies*/import java.io.*;import java.util.*;//networkimport java.net.*;import java.nio.*;import java.nio.channels.*;import java.nio.channels.spi.*;import java.nio.charset.*;public abstract class ChannelCallback{	//corresponding channel	private SocketChannel channel;		//associated Server object	private Server server = null;		//constructor	public ChannelCallback(SocketChannel channel,Server server)	{		this.channel = channel;				this.server = server;	}		//retrieval functions	public SocketChannel getChannel()	{		return channel;	}		public Server getServer()	{		return server;	}	}

/*author: gamediaceo@yahoo.comdescription: Read/Write Callback. Called whenever a socket is ready for reading/writing*//*dependencies*/import java.io.*;import java.util.*;//networkimport java.net.*;import java.nio.*;import java.nio.channels.*;import java.nio.channels.spi.*;import java.nio.charset.*;public class ReadWriteCallback extends ChannelCallback{	final static int BUFFER_SIZE=1024;		//storage for incoming data	StringBuffer incoming;		CharsetDecoder asciiDecoder;		//constructor	public ReadWriteCallback(SocketChannel channel,Server server,CharsetDecoder asciiDecoder)	{		super(channel,server);					incoming = new StringBuffer();				this.asciiDecoder = asciiDecoder;	}			public void read() throws Exception	{		ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);				//get the data in the buffer		int numBytes = getChannel().read(buffer);				//see if it's finished		if (numBytes == -1)		{			getChannel().close();			return;		}				buffer.flip();				//decode		//do the actual decoding		String result = asciiDecoder.decode(buffer).toString();				incoming.append(result);				if (incoming.indexOf("\n") != -1)		{			execute();		}			}		protected void execute() throws Exception	{		//relay to the rest of the clients		Set callbacks = getServer().getChannelCallbacks();					ByteBuffer response = ByteBuffer.wrap(incoming.toString().getBytes("US-ASCII"));				System.out.print(incoming);				for (Iterator i=callbacks.iterator();i.hasNext(); )		{			ChannelCallback callback = (ChannelCallback)i.next();			callback.getChannel().write(response);			response.flip();					}				incoming.setLength(0);				}}

/*name: SimpleChatdesc: main class@author: gamediaceo@yahoo.com*/import java.io.*;import java.util.*;public class SimpleChat{	//the port the server listens on	final static int LISTEN_PORT = 42040;		Server server = null;		public static void main(String[] args)	{		//create a new Simple Chat object		SimpleChat simpleChat = new SimpleChat();			}		//constructor	public SimpleChat()	{		try		{						server = new Server(LISTEN_PORT);					}		catch (Exception ex)		{			ex.printStackTrace();		}			}	}