apollo-core/src/main/java/com/ctrip/framework/apollo/core/utils/StringUtils.java/StringUtils/isNumeric
class StringUtils:  public static boolean isNumeric(String str) {
    if (str == null) {
      return false;
    }
    int sz = str.length();
    for (int i = 0; i < sz; i++) {
      if (!Character.isDigit(str.charAt(i))) {
        return false;
      }
    }
    return true;
  }