private static boolean isNumeric(String str) {
    if (str == null || "".equals(str)) {
      return false;
    } else {
      for (int i = str.length(); --i >= 0; ) {
        if (!Character.isDigit(str.charAt(i))) {
          return false;
        }
      }
    }

    return true;
  }
check if the string is numeric.

@param str string need to be checked
@return whether the string is a number
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/utils/OpenFileNumUtil.java