Java/Network Protocol/ServerSocketChannel

A simple TCP server for the daytime service

/*
 * Copyright (c) 2004 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 3nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose,
 * including teaching and use in open-source projects.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book, 
 * please visit http://www.davidflanagan.ru/javaexamples3.
 */
//package je3.nio;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
/**
 * A simple TCP server for the daytime service. See RFC867 for details. This
 * implementation lacks meaningful exception handling and cannot handle UDP
 * connections.
 */
public class SimpleDaytimeServer {
  public static void main(String args[]) throws java.io.IOException {
    // RFC867 specifies port 13 for this service. On Unix platforms,
    // you need to be running as root to use that port, so we allow
    // this service to use other ports for testing.
    int port = 13;
    if (args.length > 0)
      port = Integer.parseInt(args[0]);
    // Create a channel to listen for connections on.
    ServerSocketChannel server = ServerSocketChannel.open();
    // Bind the channel to a local port. Note that we do this by obtaining
    // the underlying java.net.ServerSocket and binding that socket.
    server.socket().bind(new InetSocketAddress(port));
    // Get an encoder for converting strings to bytes
    CharsetEncoder encoder = Charset.forName("US-ASCII").newEncoder();
    for (;;) { // Loop forever, processing client connections
      // Wait for a client to connect
      SocketChannel client = server.accept();
      // Build response string, wrap, and encode to bytes
      String date = new java.util.Date().toString() + "\r\n";
      ByteBuffer response = encoder.encode(CharBuffer.wrap(date));
      // Send the response to the client and disconnect.
      client.write(response);
      client.close();
    }
  }
}