Java: round unix time (Long) to first day of the month

Question

I'm trying to round a unix time to the first day of the month in Java, but without success. Example:

1314057600 (Tue, 23 Aug 2011 00:00:00 GMT)

to

1312156800 (Mon, 01 Aug 2011 00:00:00 GMT)

The unix time I'm reading from a file and storing it as a Long inside a variable (variable named "valor"). So far I've been able to create a Java timestamp with it

LocalDateTime timestamp = LocalDateTime.ofInstant(Instant.ofEpochSecond(valor), ZoneId.systemDefault());

and create a new timestamp for the beggining of the month:

LocalDate key = LocalDate.of(timestamp.getYear(), timestamp.getMonthValue(), 1);

How do I get this new timestamp as a Long?

First thing to think about: which time zone are you interested in? Always UTC? And I assume the Gregorian calendar? — Jon Skeet, May 31 '16 at 20:23
Try [this] from an earlier post (http://stackoverflow.com/a/21247526/442256) — sfk, May 31 '16 at 20:28
Time zone is not important in this case, and yes Gregorian calendar. — Vini.g.fer, May 31 '16 at 20:32
@sfk note that the answer you link is about Joda time, whereas OP is asking about the Java 8 time API. — Andy Turner, May 31 '16 at 20:33

score 2 · Accepted Answer · edited May 31 '16 at 20:54

2

Something like this sounds like it would work:

key.atStartOfDay().atZone(ZoneId.systemDefault()).toEpochSecond()

(Assuming you want it in the system's default timezone).

edited May 31 '16 at 20:54

Sotirios Delimanolis

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answered May 31 '16 at 20:23

Andy Turner

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Perfect! My mistake is that I used LocalDate instead of LocalDateTime. LocalDate doesn't have `toEpochSecond`, only `toEpochDay`, which is not the same. – Vini.g.fer May 31 '16 at 20:30

Java: round unix time (Long) to first day of the month

1 Answers1