Unable to obtain LocalDateTime from TemporalAccessor: when trying to sort the date in the stream

Question

I want to sort the posts by date("hh:mm:ss"). but I get a mistake. Can you tell me what I did wrong?

java.time.format.DateTimeParseException: Text '12:55:36' could not be parsed: Unable to obtain LocalDateTime from TemporalAccessor: {HourOfAmPm=0, MinuteOfHour=55, SecondOfMinute=36, MicroOfSecond=0, MilliOfSecond=0, NanoOfSecond=0}

class PostX {

    int id;
    String name;
    int score;
    String timePublication;

    public PostX(int id, String name, int score, String timePublication) {
        this.id = id;
        this.name = name;
        this.score = score;
        this.timePublication = timePublication;
    }

    public static void main(String[] args) {

        List<PostX> posts = List.of(
                new PostX(1,"post1", 10, "20:55:36"),
                new PostX(2,"post2", 0, "12:55:36"),
                new PostX(3,"post3", 100, "19:55:36"),
                new PostX(4,"post4", 1000, "23:55:36"),
                new PostX(5,"post5", 10, "01:50:36"),
                new PostX(6,"post6", 3, "20:55:36"),
                new PostX(7,"post7", 4, "20:15:36"),
        );
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("hh:mm:ss");
        List<PostX> posts1 = posts.stream()
                .sorted(Comparator.comparing(o -> LocalDateTime.parse(o.timePublication, formatter))).limit(5).toList();
    }
}

Use `LocalTime` or even `Instant` or some other proper date-time typo for your time of publication. Not string. It will make sorting much easier. And you can always format back into a string for presentation. — Ole V.V., May 14 '23 at 11:23
Many similar questions have been posted and answered already. So search. Only in your search skip by any answers using `SimpleDateFormat` and/or `Date` since those classes were troublesome and are now outdated and should not be used any more. — Ole V.V., May 14 '23 at 11:25
You have got two mistakes: (1) Using lower case `hh` for hour of day. Format pattern letters are case sensitive, and you need upper case `HH`. (2) Trying to parse a time of day without a date into a `LocalDateTime`. As the mńame suggests, for a `LocalDateTime` you need both a date and a time of day. A quick solution may be instead to use the `LocalTime` class I mentioned before. — Ole V.V., May 14 '23 at 11:29
by the way. it works. But I don't need to sorted(new Comparator<>() { @Override public int compare(PostX o1, PostX o2) { return o2.timePublication.compareTo(o1.timePublication); } }) — R Zav, May 14 '23 at 11:30
Yes, that should work since the lexicographic ordering of your strings agrees with chronological order. Only you are not getting the validation that you would get from parsing into a `LocalTime`. If someone happens to type `3:34:45` instead of `03:34:45`, a funny ordering will occur that you will have a hard time explaining. Terser: `.sorted(Comparator.comparing(PostX::getTimePublication))` (assuming you are defining that getter). — Ole V.V., May 14 '23 at 11:32
thank you. I replaced hh with HH and LocalDateTime with LocalTime - everything works! — R Zav, May 14 '23 at 11:37
While I didn’t downvote, the downvotes may be because of lack of demonstrated search and research. On the plus side you have given us expected behaviour, clear error message from your exception and a small and reproducible example, that all helps anyone trying to help you. — Ole V.V., May 14 '23 at 11:53

WJS · Answer 1 · 2023-06-11T19:14:24.657

You need to:

change your formatter hours to HH for 24 hour clock.
use LocalTime, not LocalDateTime.

To easily display the values, you can override toString() in your class. Here is one possible format.

 @Override
 public String toString() {
     return String.format(
             "PostX [id=%s, name=%s, score=%s, timePublication=%s]", id,
             name, score, timePublication);
 }

Then do the following:


List<PostX> posts1 = posts.stream()
                .sorted(Comparator.comparing(o->LocalTime.parse(o.timePublication, formatter)))
                .limit(5).toList();

posts1.forEach(System.out::println);

prints

PostX [id=5, name=post5, score=10, timePublication=01:50:36]
PostX [id=2, name=post2, score=0, timePublication=12:55:36]
PostX [id=3, name=post3, score=100, timePublication=19:55:36]
PostX [id=7, name=post7, score=4, timePublication=20:15:36]
PostX [id=1, name=post1, score=10, timePublication=20:55:36]

Unable to obtain LocalDateTime from TemporalAccessor: when trying to sort the date in the stream

1 Answers1