Android : sockettimeoutexception causing app hang

I am trying to ping the server in asynk task but the i am getting sockettimeout exception when i enter a invalid port number so that causes app hang. Post method of the asynk task is never called & app does not respond may i know why it happening. I am using the following code for this purpose.

private class UrlDataProvider3 extends AsyncTask<String, Void, String>

{

String ret="";
int checkStatus;
Boolean exception=false;
@Override
protected String doInBackground(String... url) 
{

    HttpURLConnection con = null;

    try 
      { 

        Log.i("RAE", "urlData"+url[0]);
        HttpURLConnection.setFollowRedirects(true);
         con = (HttpURLConnection) new URL(url[0]).openConnection();
             con.setRequestMethod("POST");
          con.setConnectTimeout(20000);




      }


    catch (IOException e)
      {


        if(e.toString().contains("java.net.SocketTimeoutException:"))
        {



           log.i("Hello","Exception Occurs");

        }



      }



return ret;
}
@Override
protected void onPostExecute(String result) {
    // TODO Auto-generated method stub
    super.onPostExecute(result);
    Log.i("RAE"," Asyc finished");

}