JSR-310 - parsing seconds fraction with variable length

Question

Is there a way how to create JSR-310 formatter that is able to parse both following date/times with variable length of seconds fraction?

2015-05-07 13:20:22.276052

or

2015-05-07 13:20:22.276

Example code:

DateTimeFormatter formatter
= new java.time.format.DateTimeFormatterBuilder()
        .append( java.time.format.DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss") )
        .appendOptional( java.time.format.DateTimeFormatter.ofPattern(".SSSSSS") )
        .toFormatter();
formatter.parse("2015-05-07 13:20:22.276052", LocalDateTime::from);

score 61 · Accepted Answer · edited May 23 '17 at 11:47

61

This solves the problem:

DateTimeFormatter formatter = new DateTimeFormatterBuilder()
    .appendPattern("yyyy-MM-dd HH:mm:ss")
    .appendFraction(ChronoField.MICRO_OF_SECOND, 0, 6, true)
    .toFormatter();

System.out.println(LocalDateTime.parse("2015-05-07 13:20:22.276052", formatter));
System.out.println(LocalDateTime.parse("2015-05-07 13:20:22.276", formatter));
System.out.println(LocalDateTime.parse("2015-05-07 13:20:22", formatter));

// output
2015-05-07T13:20:22.276052
2015-05-07T13:20:22.276
2015-05-07T13:20:22

The answer by JiriS is incorrect, as it uses appendValue whereas the correct way is to use DateTimeFormatterBuilder.appendFraction (which also handles the decimal point). The difference can be seen in the second system out, where appendValue incorrectly parses "2015-05-07T13:20:22.000276".

When parsing, LocalDateTime.parse(str, formatter) is a neater approach than using the formatter directly in most cases.

When using the builder, take advantage of appendPattern() and optionalStart() to keep things neat.

edited May 23 '17 at 11:47

Community

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1

answered May 07 '15 at 17:05

JodaStephen

60,927
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Here you recommend using `LocalDateTime.parse` rather than using the formatter directly. Yet the doc for [`DateTimeFormatter.parse`](http://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html#parse-java.lang.CharSequence-java.time.temporal.TemporalQuery-) says just the opposite: “Most applications should use this method for parsing.” … `LocalDateTime dt = parser.parse(str, LocalDateTime::from);` – Basil Bourque Feb 05 '16 at 01:38
I see the confusion. The phrase "Most applications should use this method for parsing" is wrt the other parse methods in `DateTimeFormatter`. It wasn't intended as a comparison against the `parse()` methods on classes like `LocalDate`. Thus my answer is correct, users should prefer `LocalDate.parse` to `DateTimeFormatter.parse`. – JodaStephen Feb 08 '16 at 12:01
3

Is there a way to create such a formatter with **only** a pattern string? – Jun 01 '16 at 18:58
2

No. Patterns are a subset of the possible formatters. – JodaStephen Jun 03 '16 at 13:31
FYI to people seeing this years after it was written - that `appendFraction` signature does not appear to be in the latest couple of releases (at least on Maven Central, 2.9.9+). I couldn't find any alternative that worked for microseconds. – micseydel Jun 14 '18 at 21:37

score 1 · Answer 2 · answered May 07 '15 at 14:11

1

And this one works

DateTimeFormatter formatter
= new java.time.format.DateTimeFormatterBuilder()
        .append( java.time.format.DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss") )
        .appendOptional(
                new java.time.format.DateTimeFormatterBuilder()
                    .appendLiteral('.')
                    .appendValue( ChronoField.MICRO_OF_SECOND, 1, 6, SignStyle.NOT_NEGATIVE).toFormatter())
        .toFormatter();

answered May 07 '15 at 14:11

JiriS

6,870
5
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1

This Answer’s use of `appendValue` does not work in all cases. See the [Answer by JodaStephen](http://stackoverflow.com/a/30107522/642706) for details. – Basil Bourque Feb 05 '16 at 01:40

score 1 · Answer 3 · answered Oct 15 '22 at 18:12

The accepted answer is written by the architect of modern date-time API and is the most elegant way to solve this problem. My answer shows an alternative way to solve this problem.

This solution leverages a feature of DateTimeFormatter that allows specifying optional units using square brackets.

Demo:

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;
import java.util.stream.Stream;

public class Main {
    public static void main(String[] args) {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern(
                "yyyy-MM-dd HH:mm:ss[.[SSSSSSSSS][SSSSSSSS][SSSSSSS][SSSSSS][SSSSS][SSSS][SSS][SS][S]]",
                Locale.ENGLISH);

        // Test
        Stream.of(
                "2015-05-07 13:20:22.123456789",
                "2015-05-07 13:20:22.276052",
                "2015-05-07 13:20:22.276",
                "2015-05-07 13:20:22"
        ).forEach(s -> System.out.println(LocalDateTime.parse(s, formatter)));
    }
}

Output:

2015-05-07T13:20:22.123456789
2015-05-07T13:20:22.276052
2015-05-07T13:20:22.276
2015-05-07T13:20:22

Learn more about the modern date-time API from Trail: Date Time.

score 0 · Answer 4 · edited Jan 06 '22 at 07:57

Parsing fails with a datetime without any ":" characters:

    DateTimeFormatter formatter = new DateTimeFormatterBuilder()
            .appendPattern("yyyyMMddHHmmss")
            .appendFraction(ChronoField.MICRO_OF_SECOND, 0, 9, false)
            .toFormatter();
        System.out.println(LocalDateTime.parse("20150507132022123", formatter));

Edit: it was appendFraction() which expects "." character.

JSR-310 - parsing seconds fraction with variable length

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