datetime在java中如何将时间舍入到最近的四分之一小时？

Question

考虑到今天的时间，例如下午2点24分，我如何才能将其调整到下午2点30分

同样地，如果时间是下午2:17，我怎样才能把它调到下午2:15

Answer 1

很简单，把1970年以来四分之一的数字取为两倍，四舍五入，再乘以15分钟：

long timeMs = System.System.currentTimeMillis();

long roundedtimeMs = Math.round( (double)( (double)timeMs/(double)(15*60*1000) ) ) * (15*60*1000) );

用它设置日期或日历对象

Answer 2

如果您只想进行取整，这是一个更可读的版本，使用Java Time API：

LocalDateTime time = LocalDateTime.now();
LocalDateTime lastQuarter = time.truncatedTo(ChronoUnit.HOURS)
                                .plusMinutes(15 * (time.getMinute() / 15));

输出：

2016-11-04T10:58:10.228

2016-11-04T10:45:00

Answer 3

Java8的注释实现。接受任意舍入单位和增量：

 public static ZonedDateTime round(ZonedDateTime input, TemporalField roundTo, int roundIncrement) {
    /* Extract the field being rounded. */
    int field = input.get(roundTo);

    /* Distance from previous floor. */
    int r = field % roundIncrement;

    /* Find floor and ceiling. Truncate values to base unit of field. */
    ZonedDateTime ceiling = 
        input.plus(roundIncrement - r, roundTo.getBaseUnit())
        .truncatedTo(roundTo.getBaseUnit());

    ZonedDateTime floor = 
        input.plus(-r, roundTo.getBaseUnit())
        .truncatedTo(roundTo.getBaseUnit());

    /*
     * Do a half-up rounding.
     * 
     * If (input - floor) < (ceiling - input) 
     * (i.e. floor is closer to input than ceiling)
     *  then return floor, otherwise return ceiling.
     */
    return Duration.between(floor, input).compareTo(Duration.between(input, ceiling)) < 0 ? floor : ceiling;
  }

资料来源：我自己

Answer 4

四舍五入

您需要使用模来截断四分之一小时：

Date whateverDateYouWant = new Date();
Calendar calendar = Calendar.getInstance();
calendar.setTime(whateverDateYouWant);

int unroundedMinutes = calendar.get(Calendar.MINUTE);
int mod = unroundedMinutes % 15;
calendar.add(Calendar.MINUTE, mod < 8 ? -mod : (15-mod));

正如EJP所指出的，这也是可以的（替换最后一行，仅当日历为lenient时有效）：

calendar.set(Calendar.MINUTE, unroundedMinutes + mod);

---

改进

如果希望精确，还必须截断较小的字段：

calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);

您还可以使用DateUtils.truncate()from Apache Commons / Lang来执行以下操作：

calendar = DateUtils.truncate(calendar, Calendar.MINUTE);