Convert a datatime in UTC to epoch time (seconds)

Question

I want to convert a timestamp in UTC, e.g. May 27, 2020, 22:35 (UTC) to epoch seconds. I will be hard coding the time in my code, so don't need to parse any string. I am using the Calendar class as follows:

Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
calendar.set(2020, Calendar.MAY, 22, 22, 35);
calendar.getTimeInMillis();

The epoch time is correct to the second level, but the milliseconds part seems random on every run. Example run output:

Time : 1590618900110

Is there a way I can set the millisecond to zero in Calendar object, or a better option, possibly from the java.time framework?

Edit:

The following worked fine for me, since I am hardcoding the UTC time in code:

Instant instant = Instant.parse("2020-05-27T22:35:00.00Z");
long timeInMillisEpoch = instant.toEpochMilli();

Thank you, Ahmed.

java.time is the better Choice. Do not longer use the old calendar api. — Jens, May 27 '20 at 16:47
[Convert a date format in epoch](https://stackoverflow.com/a/30830088/13527856) — MarcoLucidi, May 27 '20 at 16:53
@MarcoLucidi Since I know the exact datetime, that solution is an overkill. Found an easier one. Thanks. — Ahmed A, May 27 '20 at 16:56

MarcoLucidi · Answer 1 · 2020-05-27T17:50:57.590

2

since you already know the "exact datetime" and I guess you want to avoid the parsing, you can use this .of() method from java.time.OffsetDateTime, e.g.:

$ jshell

jshell> import java.time.*

jshell> OffsetDateTime odt = OffsetDateTime.of(2020, 5, 27, 22, 35, 0, 0, ZoneOffset.UTC)
odt ==> 2020-05-27T22:35Z

jshell> odt.toEpochSecond()
$14 ==> 1590618900

jshell> odt.toInstant().toEpochMilli()
$19 ==> 1590618900000

edit: rewrite following @Andreas advices

edited May 27 '20 at 17:50

answered May 27 '20 at 17:30

MarcoLucidi

2,007
1
5
8

2

Use constant [`ZoneOffset.UTC`](https://docs.oracle.com/javase/8/docs/api/java/time/ZoneOffset.html#UTC) instead of `ZoneId.of("UTC")`, which also means you should use [`OffsetDateTime`](https://docs.oracle.com/javase/8/docs/api/java/time/OffsetDateTime.html) instead of [`ZonedDateTime`](https://docs.oracle.com/javase/8/docs/api/java/time/ZonedDateTime.html). – Andreas May 27 '20 at 17:34
2

Question is asking for "epoch time (**seconds**)", so use [`offsetDateTime.toEpochSecond()`](https://docs.oracle.com/javase/8/docs/api/java/time/OffsetDateTime.html#toEpochSecond--). No need to create an `Instant` first. – Andreas May 27 '20 at 17:36
@Andreas it is not very clear if he wants seconds (title) or milliseconds (question body) so I left both examples – MarcoLucidi May 27 '20 at 17:54

Convert a datatime in UTC to epoch time (seconds)

1 Answers1