将Julian日期转换为Instant [英] Convert a Julian Date to an Instant

问题描述

我遇到了一个我希望从Julian日期转换为 java.time.Instant （如果这有意义），或者某些可以更容易理解的Java时间。我对Julian日期的理解来自阅读维基百科页面。有许多不同的变体，我试图阅读的日期使用不同的时代比其中任何一个。

I'm running into a situation where I would like to convert from a Julian date to an java.time.Instant (if that makes sense), or some Java time that can be more easily understood. My understanding of what a Julian date is comes from reading the Wikipedia page. There are bunch of different variants, and the date I am trying to read uses a different epoch than any of these.

例如，假设时代是日历（新风格）法案1750 ，朱利安日期 95906.27600694445 在这种情况下，我认为是 CE 2015年4月15日06：37：26.9 UT ，我如何从中得到一个瞬间？我需要稍后调整时区。

For example, let's say the epoch is the beginning of the Calendar (New Style) Act 1750, and the Julian date is 95906.27600694445 which in this case I believe is CE 2015 April 15 06:37:26.9 UT, how do I get an instant from this? I will need to adjust for the timezone later.

我注意到有一个名为 JulianFields ，但我不知道在哪里/如何用它。此外，我在包中看到的大多数方法都使用 int 或 long ，而不是<$ c c $ c> double 。

I noticed there is a class called JulianFields, but I don't know where/how to use it. Also, most of the methods I see in the package make use of int or long, not really anything for double.

那么，是否有一种简单的方法可以将使用不同时期的Julian日期转换为Java 8 即时（如果我的想法错误，还是其他时间）。

So, is there a simple way to convert from a Julian date using a different epoch to a Java 8 Instant (or some other time if my thinking is wrong).

推荐答案

以下是使用新Java 8类的解决方案：

Here is a solution using the new Java 8 classes:

public class JulianDay {
    private static final double NANOS_PER_DAY = 24.0 * 60.0 * 60.0 * 1000000000.0;

    // Calculate Instants for some epochs as defined in Wikipedia.
    public static final Instant REDUCED_JD =
            ZonedDateTime.of(1858, 11, 16, 12, 0, 0, 0, ZoneOffset.UTC).toInstant();
    public static final Instant MODIFIED_JD =
            ZonedDateTime.of(1858, 11, 17, 0, 0, 0, 0, ZoneOffset.UTC).toInstant();
    public static final Instant JULIAN_DATE =
            REDUCED_JD.minus(2400000, ChronoUnit.DAYS);

    private final Instant epoch;

    public JulianDay(Instant epoch) {
        super();
        this.epoch = epoch;
    }

    public Instant toInstant(double day) {
        long l = (long) day;
        return epoch
                .plus(l, ChronoUnit.DAYS)
                .plusNanos(Math.round((day - l) * NANOS_PER_DAY));
    }

    public static void main(String[] args) {
        // Use the example values from Wikipedia for 2015-09-07 13:21 UTC.
        System.out.println(new JulianDay(REDUCED_JD).toInstant(57273.05625));
        // Output: 2015-09-07T13:21:00.000000126Z
        System.out.println(new JulianDay(MODIFIED_JD).toInstant(57272.55625));
        // Output: 2015-09-07T13:21:00.000000126Z
        System.out.println(new JulianDay(JULIAN_DATE).toInstant(2457273.05625));
        // Output: 2015-09-07T13:20:59.999991953Z
    }
}

关于您询问的 JulianFields ，您可以定义这样的自定义格式化程序：

Regarding the JulianFields you asked about, you can define a custom formatter like this:

DateTimeFormatter formatter = new DateTimeFormatterBuilder()
    .appendValue(JulianFields.MODIFIED_JULIAN_DAY)
    .toFormatter().withZone(ZoneOffset.UTC);

不幸的是它不支持几天的分数：

Unfortunately it doesn't support fractions of days:

System.out.println(formatter.format(Instant.now())); // Output: 57249
System.out.println(LocalDate.from(formatter.parse("57249"))); // Output: 2015-08-15

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