Java Socket编程实例（五）- NIO UDP实践

一、回传协议接口和UDP方式实现：

1.接口：

import java.nio.channels.SelectionKey;
import java.io.IOException;

public interface EchoProtocol {
 void handleAccept(SelectionKey key) throws IOException;
 void handleRead(SelectionKey key) throws IOException;
 void handleWrite(SelectionKey key) throws IOException;
}

2.实现：

import java.net.SocketAddress;
import java.nio.channels.*;
import java.nio.ByteBuffer;
import java.io.IOException;

public class UDPEchoSelectorProtocol implements <span style="font-size: 1em; line-height: 1.5;">EchoProtocol </span><span style="font-size: 1em; line-height: 1.5;">{</span>
  private static final int ECHOMAX = 255; // Maximum size of echo datagram

  static class ClientRecord {
    public SocketAddress clientAddress;
    public ByteBuffer buffer = ByteBuffer.allocate(ECHOMAX);
  }

  public void handleAccept(SelectionKey key) throws IOException {

  }

  public void handleRead(SelectionKey key) throws IOException {
    DatagramChannel channel = (DatagramChannel) key.channel();
    ClientRecord clntRec = (ClientRecord) key.attachment();
    clntRec.buffer.clear(); // Prepare buffer for receiving
    clntRec.clientAddress = channel.receive(clntRec.buffer);
    if (clntRec.clientAddress != null) { // Did we receive something?
      // Register write with the selector
      key.interestOps(SelectionKey.OP_WRITE);
    }
  }

  public void handleWrite(SelectionKey key) throws IOException {
    DatagramChannel channel = (DatagramChannel) key.channel();
    ClientRecord clntRec = (ClientRecord) key.attachment();
    clntRec.buffer.flip(); // Prepare buffer for sending
    int bytesSent = channel.send(clntRec.buffer, clntRec.clientAddress);
    if (bytesSent != 0) { // Buffer completely written?
      // No longer interested in writes
      key.interestOps(SelectionKey.OP_READ);
    }
  }

}

二、NIO UDP客户端：

import java.net.InetSocketAddress;
import java.net.SocketException;
import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;

public class UDPEchoClientNonblocking {

  private static final int TIMEOUT = 3000; // Resend timeout (milliseconds)
  private static final int MAXTRIES = 255; // Maximum retransmissions

  public static void main(String args[]) throws Exception {
    // Convert input String to bytes using the default charset
    byte[] bytesToSend = "0123456789abcdefghijklmnopqrstuvwxyz".getBytes();

    // Create channel and set to nonblocking
    DatagramChannel datagramChannel = DatagramChannel.open();
    datagramChannel.configureBlocking(false);
    datagramChannel.socket().setSoTimeout(TIMEOUT);

    ByteBuffer writeBuf = ByteBuffer.wrap(bytesToSend);
    ByteBuffer readBuf = ByteBuffer.allocate(MAXTRIES);

    datagramChannel = datagramChannel.connect(new InetSocketAddress("127.0.0.1", 5500));

    int totalBytesRcvd = 0; // Total bytes received so far
    int bytesRcvd; // Bytes received in last read
    while (totalBytesRcvd < bytesToSend.length) {
      if (writeBuf.hasRemaining()) {
        datagramChannel.write(writeBuf);
      }
      if ((bytesRcvd = datagramChannel.read(readBuf)) == -1) {
        throw new SocketException("Connection closed prematurely");
      }
      totalBytesRcvd += bytesRcvd;
      System.out.print("."); // Do something else
    }

    System.out.println("Received: " + new String(readBuf.array(), 0, totalBytesRcvd));
    datagramChannel.close();
  }
}

三、NIO UDP服务端：

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

public class UDPEchoServerSelector {

  private static final int TIMEOUT = 3000; // Wait timeout (milliseconds)

  public static void main(String[] args) throws IOException {
    // Create a selector to multiplex client connections.
    Selector selector = Selector.open();

    DatagramChannel channel = DatagramChannel.open();
    channel.configureBlocking(false);
    channel.socket().bind(new InetSocketAddress(5500));
    channel.register(selector, SelectionKey.OP_READ, new UDPEchoSelectorProtocol.ClientRecord());

    UDPEchoSelectorProtocol echoSelectorProtocol = new UDPEchoSelectorProtocol();
    while (true) { // Run forever, receiving and echoing datagrams
      // Wait for task or until timeout expires
      if (selector.select(TIMEOUT) == 0) {
        System.out.print(".");
        continue;
      }

      // Get iterator on set of keys with I/O to process
      Iterator<SelectionKey> keyIter = selector.selectedKeys().iterator();
      while (keyIter.hasNext()) {
        SelectionKey key = keyIter.next(); // Key is bit mask

        // Client socket channel has pending data?
        if (key.isReadable())
          echoSelectorProtocol.handleRead(key);

        // Client socket channel is available for writing and
        // key is valid (i.e., channel not closed).
        if (key.isValid() && key.isWritable())
          echoSelectorProtocol.handleWrite(key);

        keyIter.remove();
      }
    }
  }

}

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