private final static String DATE_FORMAT =("yyyy-MM-dd");

    public void validate(String input) {
        if (input == null || !input.matches("\\d{4}[-]\\d{2}[-]\\d{2}")) {
            throw new InvalidDateFormatException();
        }

        try {
            DateFormat df = new SimpleDateFormat(DATE_FORMAT);
            df.setLenient(false);
            df.parse(input);

        }catch (ParseException e) {
            throw new UnknownDateFormatException();
        }



    }