public static String ipToRDNS(String hostIp)
    {

        if (containsOnlyNumbers(hostIp))
        {
            Record opt = null;
            Resolver res;
            try
            {
                res = new ExtendedResolver();
                Name name = ReverseMap.fromAddress(hostIp);
                int type = Type.PTR;
                int dclass = DClass.IN;
                Record rec = Record.newRecord(name, type, dclass);
                Message query = Message.newQuery(rec);
                Message response = res.send(query);
                Record[] answers = response.getSectionArray(Section.ANSWER);
                if (answers.length == 0)//error
                {
//                  sendMessage(channel, hostIp + " <-> " + hostIp);
                    System.out.println("ipToRdns error length ==  0");
                    return "error or no rDNS";
                }
                else
                {
                    String host = "" + answers[0].rdataToString();
                    host = host.substring(0, host.length() - 1);//remove the . at the end
                    return host;
                }

            } catch (UnknownHostException e)
            {
                return "Error: UnknownHost";
            } catch (IOException e)
            {
                e.printStackTrace();
            }

            System.out.println("ipToRdns final catch");
            return "error";
        }

        return "error";
    }

    public static boolean containsOnlyNumbers(String str)
    {

        //It can't contain only numbers if it's null or empty...
        if (str == null || str.length() == 0)
            return false;

        for (int i = 0; i < str.length(); i++)
        {

            //If we find a non-digit character we return false.
            if (!Character.isDigit(str.charAt(i)) && str.charAt(i) != '.')
                return false;
        }

        return true;
    }