Parse arbitrary length date String with DateTimeFormatter - date

Question

I am attempting to parse a date string of (almost) arbitrary length. The approach I had with SimpleDateFormat was something like this
private Date parseWithSimpleDateFormat(String dateString) throws ParseException {
String pattern = "yyyyMMddHHmmss".substring(0, dateString.length());
SimpleDateFormat format = new SimpleDateFormat(pattern);
return format.parse(dateString);
}
... which I want to do "better" with the new Date API. What I've come up with is the following
private static final DateTimeFormatter FLEXIBLE_FORMATTER = new DateTimeFormatterBuilder()
.appendPattern("yyyy[MM[dd[HH[mm[ss]]]]]")
.parseDefaulting(ChronoField.MONTH_OF_YEAR, 1)
.parseDefaulting(ChronoField.DAY_OF_MONTH, 1)
.parseDefaulting(ChronoField.HOUR_OF_DAY, 0)
.parseDefaulting(ChronoField.MINUTE_OF_HOUR, 0)
.parseDefaulting(ChronoField.SECOND_OF_MINUTE, 0)
.toFormatter();
private Date parseWithDateTimeFormatter(String dateString) {
LocalDateTime localDateTime = LocalDateTime.parse(dateString, FLEXIBLE_FORMATTER);
ZonedDateTime zonedDateTime = localDateTime.atZone(ZoneId.systemDefault());
Instant instant = zonedDateTime.toInstant();
return Date.from(instant);
}
with the following outcome
parseWithDateTimeFormatter("2016"); // works as intended
parseWithDateTimeFormatter("201605"); // Text '201605' could not be parsed at index 0
parseWithDateTimeFormatter("20160504"); // Text '20160504' could not be parsed at index 0
parseWithDateTimeFormatter("2016050416"); // Text '2016050416' could not be parsed at index 0
parseWithDateTimeFormatter("201605041636"); // Text '201605041636' could not be parsed at index 0
What am I doing wrong here, or how would I further troubleshoot this?

Answer 1

You can use this modified formatter in order to avoid parsing more than 4 digits for the year:
private static final DateTimeFormatter FLEXIBLE_FORMATTER =
new DateTimeFormatterBuilder()
.appendValue(ChronoField.YEAR, 4)
.appendPattern("[MM[dd[HH[mm[ss]]]]]")
.parseDefaulting(ChronoField.MONTH_OF_YEAR, 1)
.parseDefaulting(ChronoField.DAY_OF_MONTH, 1)
.parseDefaulting(ChronoField.HOUR_OF_DAY, 0)
.parseDefaulting(ChronoField.MINUTE_OF_HOUR, 0)
.parseDefaulting(ChronoField.SECOND_OF_MINUTE, 0)
.toFormatter();
In contrast to other fields like month (MM) etc., the year field symbol y has no limitation to four digits as indicated by count of y-letters.