Java查询MX记录

package org.cnhawk;

import org.xbill.DNS.*;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.*;

public class LookDNSMX{ 

    private Resolver resolver;
    private Cache cache;
    private int DNSCredibility;
    private static LookDNSMX instance=null;
    private Collection DNSServers = new Vector();
   
   
    //构造函数
    public LookDNSMX() throws Exception{
     this.initialize();
    }
    
 public static LookDNSMX getInstance() throws Exception{
  if(instance==null)
   instance=new LookDNSMX();
  return instance; 
 }
   //初始化
    public void initialize() throws Exception {
        DNSServers.add("10.0.1.1");
        final String serversArray[] = (String[])DNSServers.toArray(new String[0]);
        System.out.println("Current DNS server is : "+serversArray[0].toString());
        try {
            resolver = new ExtendedResolver(serversArray );
        } catch (UnknownHostException uhe) {
            throw uhe;
        }

        cache = new Cache (DClass.IN);
       
    }

    //主方法
    public synchronized Collection findMXRecords(String hostname)throws Exception {
        Record DNSAnswers[] =null;
        Collection MXServers = new Vector();
        //调用查看DNS的记录的方法,返回一个Record记录数组
        DNSAnswers=this.rawDNSLookup(hostname,false,Type.MX);
       
        if (DNSAnswers == null) {
            MXServers.add(hostname);
            System.out.println(hostname+" MX result is "+hostname+"\r");
            return MXServers;
        }
        MXRecord MXAnswers[] = new MXRecord[DNSAnswers.length];
        for (int i = 0; i < DNSAnswers.length; i++) {
            MXAnswers[i] = (MXRecord)DNSAnswers[i];
        }
     
        Comparator prioritySort = new Comparator () {
                public int compare (Object a, Object b) {
                    MXRecord ma = (MXRecord)a;
                    MXRecord mb = (MXRecord)b;
                    return ma.getPriority () - mb.getPriority ();
                }
            };

        Arrays.sort(MXAnswers, prioritySort);
        System.out.println("\n\n"+hostname+ "  MX result is:  ");
        String mxstr="";
        for (int i = 0; i < MXAnswers.length; i++) {
         mxstr=MXAnswers[i].getTarget ().toString ().trim();
            MXServers.add(mxstr.substring(0,mxstr.length()-1));
        }
        //System.out.println(hostname+ "  MX result is  \n"+mxstr);
        return MXServers;
    }
   
   
    /**
     * 根据给定的类型和主机名去查看DNS的记录
     * 返回一个Record记录数组
     *
     * @param hostname 被查看的主机名
     * @param querysent 这个查询是否已经被发送到DNS 服务器了
     * @param type 是要得到的记录类型
     */
   
    private Record[] rawDNSLookup(String hostname, boolean querysent, int type) {
      try{
        Name  name = Name.fromString(hostname, Name.root);
        short dclass = DClass.IN;
        Record [] DNSAnswers=null;
       
        SetResponse ResponseCached = cache.lookupRecords(name, type, DNSCredibility);
  if (ResponseCached.isSuccessful()) {
         
         return getDNSAnswers(ResponseCached);
        }
        else if (ResponseCached.isNXDOMAIN() || ResponseCached.isNXRRSET() || querysent) {
            return null;
        }
        else   
        {
            Record question = Record.newRecord(name, type, dclass);
            org.xbill.DNS.Message query = org.xbill.DNS.Message.newQuery(question);
            org.xbill.DNS.Message DNSresponse;
           
            try {
                DNSresponse = resolver.send(query);
            }catch (Throwable e) {
             e.printStackTrace();
                return null;
            }
               
            int rcode = DNSresponse.getHeader().getRcode();
            if (rcode == Rcode.NOERROR || rcode == Rcode.NXDOMAIN) {
                ResponseCached = cache.addMessage(DNSresponse);
                return getDNSAnswers(ResponseCached);
            }
   
            if (rcode != Rcode.NOERROR) {
                return null;
            }
        }
        return DNSAnswers;
      }catch (Exception e){
         e.printStackTrace();
         return null;
      }
       
    }
   
    private Record[] getDNSAnswers(SetResponse responseCached)
    {
        Record [] DNSAnswers=null;
  try
  {
   int answerCount = 0;
   int n = 0;
      RRset [] rrsets = responseCached.answers();
      for (int i = 0; i < rrsets.length; i++) {
          answerCount += rrsets[i].size();
      }
     
      DNSAnswers = new Record[answerCount];
      Iterator itor = null;
      for (int i = 0; i < rrsets.length; i++) {
          itor = rrsets[i].rrs();
          while (itor.hasNext()) {
              DNSAnswers[n++]= (Record)itor.next();
          }
   }
      }catch (Exception e){
         e.printStackTrace();
         return null;
      }
      return DNSAnswers;
    }
   
    //测试方法
    public static void main(String args[]){
     try{
      LookDNSMX  client= new  LookDNSMX();
      Collection col=client.findMXRecords("sina.com");
      Iterator it=col.iterator();
      while(it.hasNext())
      {
       System.out.println(it.next());
      }
      
      col=client.findMXRecords("handuancn.com");
      it=col.iterator();
      while(it.hasNext())
      {
       System.out.println(it.next());
      }
     }catch(Exception e){
      e.printStackTrace();
     }
    }
   
}