code: public static boolean isDateValid(String date, Locale locale) {
          try {
              DateFormat format = DateFormat.getDateTimeInstance(DateFormat.DEFAULT, DateFormat.DEFAULT, locale);
              format.parse(date);
              return true;
          } catch (ParseException e) {
              return false;
          }
      }
docs: Because the date passed as argument can be in java format, and because not all formats are compatible
  with joda-time, this method checks if the date string is valid with java. In this way we can use the
  proper DateTime without changing the output.
  
  @param date date passed as argument
  @return true if is a java date