udpnslookup.java

JAVA网络编程技术内幕一书的源代码

/*
 * Java Network Programming, Second Edition
 * Merlin Hughes, Michael Shoffner, Derek Hamner
 * Manning Publications Company; ISBN 188477749X
 *
 * http://nitric.com/jnp/
 *
 * Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
 * all rights reserved; see license.txt for details.
 */

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

public class UDPNSLookup {
  public static void main (String[] args) {
    if (args.length != 1)
      throw new IllegalArgumentException
        ("Syntax: UDPNSLookup <hostname>[@<nameserver>]");
    
    int atIdx = args[0].indexOf ("@");
    String nameServer = (atIdx > -1) ? args[0].substring (atIdx + 1) : "ns";
    String hostName = (atIdx > -1) ? args[0].substring (0, atIdx) : args[0];
    
    System.out.println ("Nameserver: " + nameServer);
    System.out.println ("Request: " + hostName);
    DNSQuery query = new DNSQuery (hostName, DNS.TYPE_ANY, DNS.CLASS_IN);
    try {
      boolean received = false;
      int count = 0;
      DatagramSocket socket = new DatagramSocket ();
      socket.setSoTimeout (5000);
      try {
        while (!received) {
          try {
            sendQuery (query, socket, InetAddress.getByName (nameServer));
            getResponse (query, socket);
            received = true;
          } catch (InterruptedIOException ex) {
            if (count ++ < 3) {
              System.out.println ("resend..");
            } else {
              throw new IOException ("No response received from nameserver");
            }
          }
        }
      } finally {
        socket.close ();
      }
      NSLookup.printRRs (query);
    } catch (IOException ex) {
      System.out.println (ex);
    }
  }

  public static void sendQuery (DNSQuery query, DatagramSocket socket, InetAddress nameServer) throws IOException {
    byte[] data = query.extractQuery ();
    DatagramPacket packet = new DatagramPacket
      (data, data.length, nameServer, DNS.DEFAULT_PORT);
    socket.send (packet);
  }

  public static void getResponse (DNSQuery query, DatagramSocket socket) throws IOException {
    byte[] buffer = new byte[512];
    DatagramPacket packet = new DatagramPacket (buffer, buffer.length);
    socket.receive (packet);
    query.receiveResponse (packet.getData (), packet.getLength ());
  }
}