问题
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")));
回答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).
回答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.
回答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);
来源：https://stackoverflow.com/questions/25552023/round-minutes-to-ceiling-using-java-8