// retrieves url with HEAD, measures how long it takes.
  public static long getTimeToHEAD(String url) {
    try {
      if (!url.contains("//")) url = "http://" + url;
      
      long startTime = now();
      HttpURLConnection con =
         (HttpURLConnection) new URL(url).openConnection();
      con.setRequestMethod("HEAD");
      con.getResponseCode();
      return now()-startTime;
    }
    catch (Exception e) {
       return -1;
    }
  }