关于NIO的一些疑问(mina)

mina 1.17版本
用mina的NIO API写了Server端，但是用多线程模仿多并发来进行BIO Client连接，以查看NIO性能，在大概400-600的连接的时候就会connection refused。

每个连接一个线程，当连接数达到一定数量时，对server的资源的占用会很大，在这种情况下nio会更好。但是跑下来的效果并不是很理想。NIO不就是用于提高线程的利用率，将普通socket做不到的事情，让NIO去处理。但是现象已经发生，不知道那位愿意给小弟指正，给点分析。

server端:

public class NIOServer {
	  private static final int PORT = 9999;

	    public static void main(String[] args) throws IOException {
	    	Executor threadPool = Executors.newFixedThreadPool(1500);
	        //设置buffer
	        ByteBuffer.setUseDirectBuffers(false);
	        ByteBuffer.setAllocator(new SimpleByteBufferAllocator());
	        //定义acceptor
	        IoAcceptor acceptor = new SocketAcceptor();
	        //定义config
	        SocketAcceptorConfig cfg = new SocketAcceptorConfig();
	        //设置config,加入filter
	        cfg.setReuseAddress(true);
	        cfg.getSessionConfig().setReuseAddress( true );
	        cfg.getSessionConfig().setReceiveBufferSize(1024);
	        cfg.setThreadModel(ThreadModel.MANUAL);
	       // cfg.getSessionConfig().setTcpNoDelay(true);
	        cfg.getFilterChain().addLast( "logger", new LoggingFilter() );
	        cfg.getFilterChain().addLast( "codec", new ProtocolCodecFilter( new TextLineCodecFactory( Charset.forName( "UTF-8" ))));
	        cfg.getFilterChain().addLast("exector", new ExecutorFilter(threadPool));
	        //加入port handler cfg
	        acceptor.bind( new InetSocketAddress(PORT), new ServerHandler(), cfg);
	        System.out.println("MINA server started.");
	    }


public class ServerHandler extends IoHandlerAdapter {
	public void exceptionCaught(IoSession session, Throwable t) throws Exception {
        t.printStackTrace();
        session.close();
    }

    public void messageReceived(IoSession session, Object msg) throws Exception {
        
        System.out.println("messageReceived~");
    }

    public void sessionCreated(IoSession session) throws Exception {
        System.out.println("Session created");

        if( session.getTransportType() == TransportType.SOCKET )
            ((SocketSessionConfig) session.getConfig() ).setReceiveBufferSize( 2048 );

        session.setIdleTime( IdleStatus.BOTH_IDLE, 10 );
    } 
} 

client:

public class ClientThread extends Thread {
	public void run() {
		final long threadId = this.getId();
		System.out.println("thread id = " + threadId);
		send(String.valueOf(threadId));
	}
	
	public ClientThread(String name){
		super(name);
	}

	public static void main(String[] args) {
		System.out.println(Thread.currentThread().getName());
		ClientThread thread = new ClientThread("0");
		thread.start();
//假设500个连接
		for(int i = 1 ; i < 500; i++) {
			thread = new ClientThread(String.valueOf(i));
			thread.start();
		}
		
	}
	
	public static void send(String msg) {
		
		byte[] buffer = new byte[1024];
		InetSocketAddress endpoint = new InetSocketAddress("10.10.10.105" , 9999);  
		try {
			Socket socket = new Socket();
			socket.setSoLinger(true, 2);
			socket.setTcpNoDelay(true);
			socket.setReuseAddress(true);
			socket.connect(endpoint);  
			OutputStream outputStream = socket.getOutputStream();
			boolean isGo=true;
			for(int i = 0 ; i < 1; i++) {
				buffer = ( "Threadname = "  + Thread.currentThread().getName() + " ,Thread ID = " + msg).getBytes();
				outputStream.write(buffer);
				outputStream.flush();
				Thread.sleep(30000);
			}

			socket.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}