How to change the base date for parsing two letter years with Java 8 DateTimeFormatter?

Question

If I use a pattern like d/M/yy for creating a Java 8 DateTimeFormatter (e.g. using DateTimeFormatter.ofPattern(pattern); (which I will only use for

Answer 1

You can create a custom formatter, for example for the d/M/yy pattern:

new DateTimeFormatterBuilder()
        .appendPattern("d/M/")
        .appendValueReduced(ChronoField.YEAR_OF_ERA, 2, 2, LocalDate.now().minusYears(80))

Example usage:

public static void main(String[] args) throws Exception {
  DateTimeFormatter fmt = new DateTimeFormatterBuilder()
          .appendPattern("d/M/")
          .appendValueReduced(ChronoField.YEAR_OF_ERA, 2, 2, LocalDate.now().minusYears(80))
          .toFormatter();
  parse("13/5/99", fmt);
  parse("13/5/36", fmt);
  parse("13/5/35", fmt);
  parse("13/5/34", fmt);
  parse("13/5/33", fmt);
}

private static void parse(String date, DateTimeFormatter fmt) {
  System.out.println(date + " = " + LocalDate.parse(date, fmt));
}

which prints:

13/5/99 = 1999-05-13
13/5/36 = 1936-05-13
13/5/35 = 1935-05-13
13/5/34 = 2034-05-13
13/5/33 = 2033-05-13