code: public static boolean isMustFieldValid(String field, String reg) {
          if (field == null || field.length() == 0) {
              return false;
          }
          return Pattern.matches(reg, field);
      }
docs: Validate the required field String against the regex.
  
  @param field
  the field value String.
  @param reg
  the regex.
  @return
  true if matched.