如何使用NIO套接字只写一次或“在某些命令上”？

Question

这是的chargen服务器的一个例子，我在书中发现，我正在读：

import java.nio.*; 
import java.nio.channels.*; 
import java.net.*; 
import java.util.*; 
import java.io.IOException; 

public class ChargenServer { 

    public static int DEFAULT_PORT = 19; 

    public static void main(String[] args) { 

    int port; 
    try { 
     port = Integer.parseInt(args[0]); 
    } 
    catch (Exception ex) { 
     port = DEFAULT_PORT; 
    } 
    System.out.println("Listening for connections on port " + port); 

    byte[] rotation = new byte[95*2]; 
    for (byte i = ' '; i <= '~'; i++) { 
     rotation[i-' '] = i; 
     rotation[i+95-' '] = i; 
    } 

    ServerSocketChannel serverChannel; 
    Selector selector; 
    try { 
     serverChannel = ServerSocketChannel.open(); 
     ServerSocket ss = serverChannel.socket(); 
     InetSocketAddress address = new InetSocketAddress(port); 
     ss.bind(address); 
     serverChannel.configureBlocking(false); 
     selector = Selector.open(); 
     serverChannel.register(selector, SelectionKey.OP_ACCEPT); 
    } 
    catch (IOException ex) { 
     ex.printStackTrace(); 
     return; 
    } 

    while (true) { 

     try { 
     selector.select(); 
     } 
     catch (IOException ex) { 
     ex.printStackTrace(); 
     break; 
     } 

     Set readyKeys = selector.selectedKeys(); 
     Iterator iterator = readyKeys.iterator(); 
     while (iterator.hasNext()) { 

     SelectionKey key = (SelectionKey) iterator.next(); 
     iterator.remove(); 
     try { 
      if (key.isAcceptable()) { 
      ServerSocketChannel server = (ServerSocketChannel) key.channel(); 
      SocketChannel client = server.accept(); 
      System.out.println("Accepted connection from " + client); 
      client.configureBlocking(false); 
      SelectionKey key2 = client.register(selector, SelectionKey.OP_WRITE); 
      ByteBuffer buffer = ByteBuffer.allocate(74); 
      buffer.put(rotation, 0, 72); 
      buffer.put((byte) '\r'); 
      buffer.put((byte) '\n'); 
      buffer.flip(); 
      key2.attach(buffer); 
      } 
      else if (key.isWritable()) { 
      SocketChannel client = (SocketChannel) key.channel(); 
      ByteBuffer buffer = (ByteBuffer) key.attachment(); 
      if (!buffer.hasRemaining()) { 
       // Refill the buffer with the next line 
       buffer.rewind(); 
       // Get the old first character 
       int first = buffer.get(); 
       // Get ready to change the data in the buffer 
       buffer.rewind(); 
       // Find the new first characters position in rotation 
       int position = first - ' ' + 1; 
       // copy the data from rotation into the buffer 
       buffer.put(rotation, position, 72); 
       // Store a line break at the end of the buffer 
       buffer.put((byte) '\r'); 
       buffer.put((byte) '\n'); 
       // Prepare the buffer for writing 
       buffer.flip(); 
      } 
      client.write(buffer); 
      } 
     } 
     catch (IOException ex) { 
      key.cancel(); 
      try { 
      key.channel().close(); 
      } 
      catch (IOException cex) {} 
     } 

     } 

    } 

    } 

} 

一旦客户端连接到服务器时，它继续发送字符流给客户端，并不会停止。

我很好奇，如果我想发送缓冲一次，仍然保持服务器连接到客户端。我该怎么办？

Answer 1

套接字通道几乎都是可写的。当你有一个零长度的写入时，你应该只在OP_WRITE上选择。如果你有一些东西要写，就写下来，然后检查返回值。