NIO selector写的一个小服务器server发给client的消息，client有时候收不到

[zhujun88nz]

最近才学NIO，用selector写了个小server，想让才连上的client给server发送 "Hello Server"，server收到后反回去信息"Hello Client"， 可是很多情况下client收不到这个信息。 代码如下
Server：

public class Server {

    private static final int TIME_OUT = 3000;
    public static final int BUFFSIZE = 10240;
    public static final int PORT = 9999;
    private Selector selector;
    private ServerSocketChannel serverSocketChannel;
    private SocketChannel lastChannel;
    private boolean connecting;
    
    public static void main(String[] args) throws IOException {
        Server server = new Server();
        server.selecting();
    }

    public Server() throws IOException {
        selector = Selector.open();

        serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.socket().bind(new InetSocketAddress(PORT));
        serverSocketChannel.configureBlocking(false);
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        connecting = true;
    }

    private void selecting() throws IOException {
        while (connecting) {
            if (selector.select(TIME_OUT) == 0) {
                System.out.println("idle");
                continue;
            }

            Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
            while (iterator.hasNext()) {
                SelectionKey key = iterator.next();
                iterator.remove();

                if (key.isAcceptable()) {
                    SocketChannel channel = ((ServerSocketChannel) (key.channel())).accept();
                    channel.configureBlocking(false);
                    channel.register(selector, SelectionKey.OP_READ);
                    System.out.println("accept a client");
                } else if (key.isReadable()) {
                    SocketChannel channel = (SocketChannel) key.channel();
                    ByteBuffer buf = ByteBuffer.allocate(BUFFSIZE);
                    int byteRead = channel.read(buf);
                    if(byteRead == -1){
                        channel.close();
                        key.cancel();
                    } else if(byteRead>0){
                        buf.flip();
                        System.out.println(new String(buf.array()));
                        lastChannel = channel;
                        key.interestOps(SelectionKey.OP_WRITE | SelectionKey.OP_READ);
                        System.out.println("read from a client");
                    }
                } else if (key.isWritable() && key.isValid()) {
                    ByteBuffer writeBuffer = ByteBuffer.wrap("Hello Client".getBytes());
                    SocketChannel channel = (SocketChannel) key.channel();
                    channel.write(writeBuffer);
                    System.out.println("write to a client");
                    key.interestOps(SelectionKey.OP_READ);
                }
            }
        }
    }
}

Client：

public class Client {
    
    private SocketChannel socketChannel;
    private boolean running;
    
    public static void main(String[] args) throws IOException {
        Client client = new Client();
        client.connect();
        client.send();
        client.receive();
    }
    
    public Client() throws IOException{
        running = true;
        socketChannel = SocketChannel.open();
        socketChannel.configureBlocking(false);
    }
    
    private void connect() throws IOException{
        InetSocketAddress isa = new InetSocketAddress(Server.PORT);
        if(!socketChannel.connect(isa)){
            while(!socketChannel.finishConnect())
                System.out.println("connecting");
        }
    }
    
    private void send() throws IOException{
        ByteBuffer sendBuffer = ByteBuffer.allocate(Server.BUFFSIZE);
        sendBuffer.clear();
        sendBuffer.put("Hello server".getBytes());
        sendBuffer.flip();
        while(sendBuffer.hasRemaining())
            socketChannel.write(sendBuffer);
        
        System.out.println("sent");
//        socketChannel.close();
    }
    
    private void receive() throws IOException{
        ByteBuffer receiveBuff = ByteBuffer.allocate(Server.BUFFSIZE);
        while(running){
            if(socketChannel.read(receiveBuff)==-1)
                socketChannel.close();
            else if(socketChannel.read(receiveBuff)>0){
                receiveBuff.flip();
                System.out.println(new String(receiveBuff.array()));
                receiveBuff.compact();
                System.out.println("received");
            } 
        }
    }
}

请高手指点。