当客户端连接关闭时，服务器select()不会阻塞，然后一直分发读就绪操作，且读到的字节长度都是0，这是什么情况。

服务器代码

public class NIOServerTest {
    public static void main(String[] args) {
        try {
            ServerSocketChannel serverChannel = ServerSocketChannel.open();
            serverChannel.bind(new InetSocketAddress(666));
            serverChannel.configureBlocking(false);
            Selector selector = Selector.open();
            serverChannel.register(selector,SelectionKey.OP_ACCEPT);
            while(true){
                int count = selector.select(); //阻塞
                if(count>0){
                    Set<SelectionKey> keys = selector.selectedKeys();
                    Iterator<SelectionKey> iterator = keys.iterator();
                    while(iterator.hasNext()){
                        SelectionKey key = iterator.next();
                        iterator.remove();
                        if(key.isAcceptable()){
                            System.out.println("client connect");
                            ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();
                            SocketChannel sc = serverSocketChannel.accept();
                            sc.configureBlocking(false);
                            sc.register(selector, SelectionKey.OP_READ);
                        }
                        if(key.isReadable()){
                            SocketChannel socketChannel = (SocketChannel) key.channel();
                            ByteBuffer buffer = ByteBuffer.allocate(512);
                            socketChannel.read(buffer);
                            buffer.flip();
                            System.out.println("on read size:"+buffer.remaining());
                        }
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

客户端代码

public class NIOClientTest{
    public static void main(String[] args) throws UnknownHostException, IOException{
        try {
            Socket socket = new Socket("127.0.0.1",666);
            try(OutputStreamWriter output = new OutputStreamWriter(socket.getOutputStream());){
                output.write(1);
                output.flush();
            }catch (Exception e) {
                e.printStackTrace();
            }
            socket.close();
        } catch (Exception e1) {
            e1.printStackTrace();
        } 
    }
}