Round minutes to ceiling using Java 8

Question

So I'm lucky enough to use Java 8 and the new time APi but I don't see any rounding functions...

Basically if the time is...

2014-08-28T10:01.00.000 ----> 2014-08-28T10:02.00.000
2014-08-28T10:01.10.123 ----> 2014-08-28T10:02.00.000
2014-08-28T10:01.25.123 ----> 2014-08-28T10:02.00.000
2014-08-28T10:01.49.123 ----> 2014-08-28T10:02.00.000
2014-08-28T10:01.59.999 ----> 2014-08-28T10:02.00.000

This seems to be ok, but is it right?

LocalDateTime now =  LocalDateTime.now(Clock.systemUTC());
LocalDateTime newTime =  now.plusMinutes(1);

System.out.println(newTime.toString());
System.out.println(newTime.format(DateTimeFormatter.ofPattern("yyyy-dd-MM'T'HH:mm:00.000")));

Answer 1

The java.time API does not support rounding to ceiling, however it does support rounding to floor (truncation) which enables the desired behaviour (which isn't exactly rounding to ceiling):

LocalDateTime now =  LocalDateTime.now();
LocalDateTime roundFloor =  now.truncatedTo(ChronoUnit.MINUTES);
LocalDateTime roundCeiling =  now.truncatedTo(ChronoUnit.MINUTES).plusMinutes(1);

In addition, there is a facility to obtain a clock that only ticks once a minute, which may be of interest:

Clock minuteTickingClock = Clock.tickMinutes(ZoneId.systemDefault());
LocalDateTime now =  LocalDateTime.now(minuteTickingClock);
LocalDateTime roundCeiling =  now.plusMinutes(1);

This clock will automatically truncate minutes to floor (although it is specified such that it may return a delayed cached value). Note that a Clock may be stored in a static variable if desired.

Finally, if this is a common operation that you want to use in multiple places, it is possible to write a library TemporalAdjuster function to perform the rounding. (Adjusters can be written once, tested, and made available as a static variable or method).

Answer 2

LocalDateTime newTime = now.plusMinutes(1).minusNanos(1).withSecond(0).withNano(0);

This will round up to the nearest minute, acting as a ceiling function with minutes as the integer part.

Answer 3

java.time (the new time API in Java 8) has no rounding features like some other libraries. You try to use formatting to round on String-level. If you want to round the time objects however, then you can do this rounding manually:

LocalDateTime now =  LocalDateTime.now(Clock.systemUTC());
LocalDateTime newTime =  now.plusMinutes(1).withSecond(0).withNano(0);

By the way, you surely meant floor, not ceiling, isn't it?

Update:

I have found this slightly better way for setting to floor (obviously the only rounding feature, ceiling is not supported):

LocalDateTime now =  LocalDateTime.now(Clock.systemUTC());
LocalDateTime newTime =  now.plusMinutes(1).truncatedTo(ChronoUnit.MINUTES);