echoudpserver.java

21天学通java的示例程序源代码

package com.wrox;

import java.net.*;
import java.io.*;

/** Server implementing the RFC 862 UDP echo protocol */
public class EchoUDPServer extends Thread {

  /** Standard UDP echo service port defined in RFC 862 (port=7) */
  public static int STANDARD_ECHO_PORT = 7;

  /** Default number of milliseconds between termination checks */
  public static int DEFAULT_TERMINATION_CHECK_MILLIS = 5000;

  /** The maximum UDP data length possible (in bytes) */
  public static int MAX_UDP_DATA_LENGTH = 65508;

  /** UDP socket used to receive echo requests */
  protected DatagramSocket socket;
  
  /** Controls execution of the datagram receive thread */
  protected boolean isActive;

  /** 
   * Constructs an RFC 862 UDP Echo Protocol server
   *
   * @param port - the UDP port number used for binding
   * @exception SocketException - if the UDP datagram socket creation fails
   * @exception SecurityException - if permission to accept connections
   *                                is refused by the security manager.
   */
  public EchoUDPServer(int port) throws SocketException {
    super("EchoServer(" + port + ")");

    socket = new DatagramSocket(port);
    socket.setSoTimeout(DEFAULT_TERMINATION_CHECK_MILLIS);
    isActive = true;

    start();
  }

  /** Requests asynchronous termination of the receiving thread */
  public void terminate() {
    isActive = false;
  }

  /**
   * Main thread receives and immediately sends back any data received.
   * <p>
   * Loop termination controlled by the terminate() method.
   */
  public void run() {
    System.out.println("Echo server bound to port " +
                       socket.getLocalPort());

    DatagramPacket receivePacket =
      new DatagramPacket(new byte[MAX_UDP_DATA_LENGTH],
                         MAX_UDP_DATA_LENGTH);

    while(isActive) {
      try {
        // Reset the receivePacket length to the byte array length
        receivePacket.setLength(MAX_UDP_DATA_LENGTH);

        // Wait to receive echo request (may also time-out)
        socket.receive(receivePacket);

        // We just send the packet back to the sender (already marked in
        // the packet by the receive method)
        socket.send(receivePacket); 
      } catch (InterruptedIOException e) {
        // ignore (used to check for termination)
      } catch (Throwable e) {
        // ignore
      }
    }
    try { socket.close(); } catch (Throwable e) { }
  }
  
  /** Command-line utility for performing UDP echo requests. */
  public static void main(String[] args) {
    if (args.length > 1) {
      System.err.println("Usage: EchoUDPServer { <port> }");
      System.exit(1);
    }

    int port = STANDARD_ECHO_PORT;
    if (args.length == 1) {
      try {
        port = Integer.parseInt(args[0]);
      } catch (NumberFormatException e) {
        System.err.println("EchoUDPServer: invalid port number " + args[0]);
        System.exit(1);
      }
    }
    
    try {
      EchoUDPServer server = new EchoUDPServer(port);
      server.join();
    } catch (Throwable e) {
      System.err.println("EchoUDPServer: " + e);
      System.exit(1);
    }
  }
}