Сокет сервер с использованием Java NIO

import java.io.*;
import java.net.*;
import java.nio.*;
import java.util.*;
import java.nio.channels.*;
 
class TestServer
{
  private static final int PORT = 4444;
  private static final int BUFFER_SIZE = 1024;
 
  public static void main(String[] arg)
  {
    try
    {
      // Instead of creating a ServerSocket, create a ServerSocketChannel:
      ServerSocketChannel ssc = ServerSocketChannel.open();
 
      // Set it to non-blocking, so we can use select:
      ssc.configureBlocking(false);
 
      // Get the Socket connected to this channel, and bind it to the listening port:
      ServerSocket ss = ssc.socket();
      ss.bind(new InetSocketAddress(PORT));
 
      // Create a new Selector for selecting:
      Selector selector = Selector.open();
 
      // Register the ServerSocketChannel, so we can listen for incoming connections:
      ssc.register(selector, SelectionKey.OP_ACCEPT);
 
      ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);
 
      while(true)
      {
        // See if we''ve had any activity - either an incoming connection,
        //  or incoming data on an existing connection:
        int num = selector.select();
 
        // If we don''t have any activity, loop around and wait again:
        if(num == 0) continue;
 
        // Get the selectedKeys corresponding to the activity
        // that has been detected, and process them
        // one by one:
        Set selectedKeys = selector.selectedKeys();
        Iterator selectedKeysIterator = selectedKeys.iterator();
 
        while(selectedKeysIterator.hasNext())
        {
          // Get a selectedKey representing one of bits of I/O activity:
          SelectionKey selectedKey = (SelectionKey) selectedKeysIterator.next();
 
          // What kind of activity is selectedKeysIterator ?
          if((selectedKey.readyOps() & SelectionKey.OP_ACCEPT) == SelectionKey.OP_ACCEPT)
          {
            // It''s an incoming connection.
            // Register this socket with the Selector
            // so we can listen for input on selectedKeysIterator:
            Socket s = ss.accept();
 
            // Make sure to make selectedKeysIterator non-blocking, so we can
            // use a selector on selectedKeysIterator:
            SocketChannel sc = s.getChannel();
            sc.configureBlocking(false);
 
            // Register selectedKeysIterator with the selector, for reading:
            sc.register(selector, SelectionKey.OP_READ);
          }
          else if((selectedKey.readyOps() & SelectionKey.OP_READ) == SelectionKey.OP_READ)
          {
 
            SocketChannel sc = null;
 
            try
            {
              // It''s incoming data on a connection, so process selectedKeysIterator:
              sc = (SocketChannel) selectedKey.channel();
 
              // Process the incoming data:
              buffer.clear();
              sc.read(buffer);
              buffer.flip();
 
              // If the connection is dead, then remove selectedKeysIterator
              // from the selector and close selectedKeysIterator
              if(buffer.limit() == 0)
              {
                selectedKey.cancel();
 
                Socket s = null;
 
                try
                {
                  s = sc.socket();
                  s.close();
                }
                catch(IOException ie)
                {
                  System.err.println("Error closing socket " + s + ": " + ie);
                }