public static String createStringCode(boolean numberFlag, int length) {
      String retStr = "";     String strTable = numberFlag ? "1234567890" : "1234567890abcdefghijkmnpqrstuvwxyz";     int len = strTable.length();     retStr = "";     for (int i = 0; i < length; i++) {
          double v = Math.random() * len;         logger.info(v+"------");         retStr += strTable.charAt((int)Math.floor(v));     }     return retStr; }