Java - 从 Double 获取 LocalDateTime

Question

I am receiving this value in a Json format:

 {"time": 1643213994.7369497}

This time value is supposed to produce a DateTime value like this:

 2021-08-12T03:03:31.656050+00:00

How can I get this value parsed into a LocalDateTime object or the format above?

Answer 1

Assuming that number represents an Epoch Time, have you tried (in Java 8+) rounding it up and using

LocalDateTime myLocalDateTime = Instant.ofEpochMilli(yourTimeHere).atZone(ZoneId.systemDefault()).toLocalDateTime();

for example?

You might want to replace ZoneId.systemDefault() with the ZoneID that is relevant to you.

Answer 2

Since there's no timezone / offset information available in your source, you can convert it to an Instant and convert that to a ZonedDateTime or OffsetDateTime later.

A double like yours can be converted to an Instant using this method:

    public static Instant toInstant(double value) {
        final long epochSecond = (long) Math.floor(value);
        final long nanoAdjustment = (long) ((value % 1.0) * 1000_000_000.0);

        return Instant.ofEpochSecond(epochSecond, nanoAdjustment);
    }

You can then later convert it to a ZonedDateTime like this:

        Instant yourInstant = ...;
        ZonedDateTime zdt = yourInstant.atZone(ZoneId.systemDefault());