8

Given a FileTime fileTime, how can it be formatted in a custom way to a string?

String s = fileTime.toString() provides it in ISO format only.

String s = DateTimeFormatter.ofPattern("uuuu-MMM-dd HH:mm:ss")
                              .format(fileTime.toInstant());

throws UnsupportedTemporalTypeException: Unsupported field: Year

Museful
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  • did you mean `yyyy` instead of `uuuu` – Kal Oct 30 '15 at 00:47
  • @Kal I tried both. `yyyy` just throws `Unsupported field: Year of Era` instead of `Unsupported field: Year`. – Museful Oct 30 '15 at 00:49
  • Did you try `toMillis` instead of `toInstant`? Formatting an `Instant` requires timezone. – Kal Oct 30 '15 at 00:59
  • @Kal I tried [this](http://stackoverflow.com/questions/33366031/obtain-last-modification-date-time-of-file-as-local-date-time-string). How would one proceed with the result of `toMillis`? – Museful Oct 30 '15 at 01:12
  • ah yes. I think your best bet is to just attach timezone to the DateTimeFormatter -- http://stackoverflow.com/questions/25229124/format-instant-to-string – Kal Oct 30 '15 at 01:17

5 Answers5

6

Personally I find the error message "Unsupported field: Year" misleading. The real cause is missing timezone. This information is needed to help the formatter to internally convert the given instant to a human-time-representation. Solution: Supply the timezone. Then formatting or parsing an Instant is supported - in contrast to the answer of @flo.

Printing:

String s = 
  DateTimeFormatter.ofPattern("uuuu-MMM-dd HH:mm:ss", Locale.ENGLISH)
    .withZone(ZoneId.systemDefault())
    .format(Instant.now());
System.out.println(s); // 2015-Oct-30 15:22:32

Parsing:

The reverse procedure - parsing - does unfortunately not work the same direct way because the format engine of java.time is designed such that the formatter only returns a raw TemporalAccessor which needs to be converted to the real required type. Example:

Instant instant =
  Instant.from(
    DateTimeFormatter.ofPattern("uuuu-MMM-dd HH:mm:ss", Locale.ENGLISH)
    .withZone(ZoneId.systemDefault())
    .parse("2015-Oct-30 15:22:32"));
System.out.println("=>" + instant); // 2015-10-30T14:22:32Z

If the input to be parsed contains a timezone offset or an identifier then you can modify the pattern (symbols x, X, z, Z, VV etc.) and leave out the call to withZone(...), and in case of offsets - you really should leave out that call because otherwise the formatter will not use the timezone offset of your input but the supplied one zone (a pitfall I observed in my own tests).

Meno Hochschild
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4

You cannot format an Instant using a DateTimeFormatter instance querying the year.

An Instant is representing a single point on the time line. That's why it is not possible to give a correct/unique answer to the question "what's the year/day/time?". It depends on where on the world the question is asked: In New York it differs from Sidney. But your DateTimeFormatter is asking exactly this question. And that is why you get an UnsupportedTemporalTypeException.

You have to convert the Instance to a LocalDateTime at least:

System.out.println(timestampFormatter.format(
    LocalDateTime.ofInstant(fileTime.toInstant(), ZoneId.systemDefault()));
flo
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2

Formatting an Instant requires a time-zone. This can be achieved using withZone(ZoneId):

String s = DateTimeFormatter.ofPattern("uuuu-MMM-dd HH:mm:ss")
                 .withZone(ZoneId.systemDefault())
                 .format(fileTime.toInstant());
JodaStephen
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1

If your time looks like this 

2015-01-01T10:10:09

Use

yyyy-MM-dd'T'HH:mm:ss
Enzokie
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1

ZonedDateTime can parse the default string that you get from a FileTime.toString(): (supply your own 'path' in the code snippet below)

FileTime fileTime = Files.getLastModifiedTime(path);
ZonedDateTime zonedDateTime = ZonedDateTime.parse(fileTime.toString());
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("EEEE, MMMM d, yyyy   HH:mm:ss");   
System.out.println(dtf.format(zonedDateTime));

Result: Saturday, April 18, 2020 13:43:29

selofain
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