How can you, in Java, compute the unix timestamp truncated to midnight?
PHP examples show making strings and then parsing them back. There has to be a cleaner way to do it in Java than that, surely?
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1Midnight in which time zone? And can you use Joda Time? – Jon Skeet May 13 '13 at 06:15
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@JonSkeet UTC and yes, I could use Joda Time although I'm not yet using it anywhere else – Will May 13 '13 at 06:18
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1If you're doing any significant amount of date/time work, I'd *thoroughly* recommend using Joda Time :) – Jon Skeet May 13 '13 at 06:25
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Note that for Java 8 you have a new date+time API which makes this much easier to do. – Thorbjørn Ravn Andersen Dec 24 '16 at 23:52
3 Answers
5
Unix timestamp starts from midnight UTC so we can do the following
Calendar c = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
c.set(Calendar.HOUR_OF_DAY, 0);
c.set(Calendar.MINUTE, 0);
c.set(Calendar.SECOND, 0);
c.set(Calendar.MILLISECOND, 0);
long unixTimeStamp = c.getTimeInMillis() / 1000;
Evgeniy Dorofeev
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For unix timestamps you can create function like this:
public long getMidnightTimestamp(long timestamp)
{
return timestamp - timestamp % 86400; // 24 * 60 * 60 sec in one day
}
And use it like this:
long currentTimestamp = System.currentTimeMillis() / 1000;
long todayMidnightTimestamp = getMidnightTimestamp(currentTimestamp);
obywatelgcc
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Leap seconds? This will be slightly imprecise i think. There have been 27 of them since 1970. (OK, forget it. unix time does no do leap seconds. That makes unix time slightly imprecise, but your trick will work 100%) – Karl May 17 '18 at 04:12
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Smart! A neat workarround without the need to rely on Calendar/Date/SimpleDateFormat – Raste Jun 16 '21 at 16:32
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Calendar c = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
c.set(Calendar.HOUR,0);
c.set(Calendar.MINUTE,0);
c.set(Calendar.SECOND,0);
c.set(Calendar.MILLISECOND,0);
long midnightUnixTimestamp = c.getTime().getTime()/1000;
David Rabinowitz
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