Forcing Java 8 LocalTime toString to report omitted values

Question

I have the following datetime helper method that converts a UTC-zoned Java 8 Date into a datetime string:

public static String dateTimeString(Date date) {
    return date.toInstant().atZone(ZoneId.of("UTC")).toLocalDateTime().toString();
}

The desired result is to always have the resultant String be formatted as:

YYYY-MM-dd'T'HH:mm:ss'Z'

Problem is, Java 8 LocalTime#toString() intentionally strips off time components that are zero. So for instance if I have a Date instance that represents June 8, 2018 at 12:35:00 UTC. Then the output of this method above is: 2018-06-08'T'12:35'Z'. Whereas I want it to contain any zeroed-out second/minute/hour components (e.g. 2018-06-08'T'12:35:00'Z').

Any ideas?

Obviously, you could create your own DateTimeFormat that formats it like this except without omission. I have no other idea. — Dreamspace President, Apr 24 '18 at 08:05
I would accept that as a solution @DreamspacePresident (+1) -- any ideas on what that code would look like? — hotmeatballsoup, Apr 24 '18 at 08:06
Possible duplicate of [Java: DateTimeFormatter fail to parse time string when seconds and milliseconds are all 0s?](https://stackoverflow.com/questions/49967139/java-datetimeformatter-fail-to-parse-time-string-when-seconds-and-milliseconds) — Ole V.V., Apr 24 '18 at 08:23
Thanks @OleV.V. (+1) however the accepted answer to that question uses `DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss:SSS")` which is not UTC-zoned. — hotmeatballsoup, Apr 24 '18 at 08:30
@hotmeatballsoup Too bad you accepted a different answer, even though it came half an hour after mine. :P — Dreamspace President, May 06 '18 at 04:57

Ole V.V. · Accepted Answer · 2018-04-24T09:09:50.450

private static DateTimeFormatter formatter = DateTimeFormatter.ofPattern("uuuu-MM-dd'T'HH:mm:ssX");

public static String dateTimeString(Date date) {
    return date.toInstant().atOffset(ZoneOffset.UTC).format(formatter);
}

Just use a fixed format pattern string to get your desired format. Let’s try it:

    System.out.println(dateTimeString(new Date(0)));
    System.out.println(dateTimeString(new Date(1_524_560_255_555L)));

This prints:

1970-01-01T00:00:00Z
2018-04-24T08:57:35Z

In the first example hours, minutes and seconds are printed even if they are 0.
In the second example milliseoncds are omitted even when they are non-zero (you see that the milliseconds value I specified ends in 555).

All of this said, the output conforms to the ISO 8601 format no matter if you have 2018-06-08T12:35Z, 2018-06-08T12:35:00Z or even 2018-06-08T12:35:00.000000000Z. So you may want to check once more whether leaving out the second works for your purpose before you take the trouble of defining your own formatter.

Link: Wikipedia article: ISO 8601

score 1 · Answer 2 · answered Apr 24 '18 at 08:30

I don't see why you portray the default output to have its letters enclosed in single quotes when Java's actual output instead looks like 2018-06-08T12:35Z, but anyway, here's the code that produces it as desired, with no omissions:

final LocalDateTime ldt = LocalDateTime.of(2018, 6, 8, 12, 35, 0);

final ZonedDateTime zdt = ZonedDateTime.of(ldt, ZoneId.of("Z"));

final DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd'''T'''HH:mm:ss''X''", Locale.US);

System.err.println(dtf.format(zdt));

Output:

2018-06-08'T'12:35:00'Z'

Personally, I'd probably prefer a format like this, containing the millis, giving time zone information not requiring additional knowledge from the user, and not having imho superfluous characters:

FORMAT: "yyyy-MM-dd HH:mm:ss'.'SSS Z"

OUTPUT: 2018-06-08 12:35:12.345 +0200

Thanks @Dreamspace President (+1)! How/where could I format this to be UTC-zoned? — hotmeatballsoup, Apr 24 '18 at 08:31
Best I can do is GMT: Replace **X** in the 4-line code, 3rd line, with **OOOO**, which changes that part of the output from **Z** to **GMT**. The JavaDocs say "GMT+8; GMT+08:00; UTC-08:00" but I was not able to ever produce it to say UTC, it always says GMT. — Dreamspace President, Apr 24 '18 at 08:38

score 0 · Answer 3 · answered Apr 24 '18 at 08:25

0

It appears that there is no out of the box solution. The simplest way would be to write your own class that extends DateTimeFormatter and override method public String format(TemporalAccessor temporal) where you would call the original method and then if needed modify the output String. See the flags 'Z' for formatter. If that flag is present then you will need to modify the original output.

answered Apr 24 '18 at 08:25

Michael Gantman

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The `DateTimeFormatter`class is final, you can’t extend (subclass) it. Also just defining your own format pattern string appears to be simpler. – Ole V.V. Apr 24 '18 at 08:25
1

@Ole V.V. - you are correct, I missed that. Then you can have your own class that will contain DateTimeFormatter class, I.e. Wrapper class. And you can write all the methods of DateTimeFormatter and deligate them to the original ones except `public String format(TemporalAccessor temporal)` where you will need to make modification to the original result as needed. A bit more work but it will do – Michael Gantman Apr 24 '18 at 08:29

Forcing Java 8 LocalTime toString to report omitted values

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