简答：

LocalDate date = LocalDate.now();
long modifiedJulianDay = date.getLong(JulianFields.MODIFIED_JULIAN_DAY);

说明：

***文章给出了朱利安日作为概念的***描述。简而言之，它是一个简单的，连续的，从某个时代起的天数，其中所选择的时代赋予变体名称。因此，修改后的朱利安日计数从1858-11-17。

The Wikipedia article gives the best description of Julian day as a concept. Put simply, it is a simple, continuous, count of days from some epoch, where the chosen epoch gives the variation its name. Thus, Modified Julian Day counts from 1858-11-17.

JSR-310日期和时间对象实现 TemporalAccessor 接口定义方法 get（TemporalField）和 getLong（TemporalField）。这些允许查询特定字段时间的日期/时间对象。提供了四个字段实现，提供Julian日变化：

JSR-310 date and time objects implement the TemporalAccessor interface which defines the methods get(TemporalField) and getLong(TemporalField). These allow the date/time object to be queried for a specific field of time. Four field implementations are provided offering Julian day variations:

• JulianFields.MODIFIED_JULIAN_DAY - 标准修改的朱利安日


• JulianFields.JULIAN_DAY - 基于午夜的标准朱利安日概念变体


• JulianFields.RATA_DIE - 基于格里高利时代的朱利安日变异


• ChronoField.EPOCH_DAY - 基于标准Java / UNIX 1970-01-01的Julian日变体

• JulianFields.MODIFIED_JULIAN_DAY - the standard Modified Julian Day
• JulianFields.JULIAN_DAY - a midnight-based variation of the standard Julian day concept
• JulianFields.RATA_DIE - a Julian day variation based on the Gregorian common era
• ChronoField.EPOCH_DAY - a Julian day variation based on the standard Java/UNIX 1970-01-01

这些字段只能与 getLong（TemporalField）一起使用，因为它们返回的数字对于 INT 。如果你调用 now.get（JulianFields.MODIFIED_JULIAN_DAY），那么将抛出一个异常：UnsupportedTemporalTypeException：get（）方法的无效字段ModifiedJulianDay，使用getLong（）而不是

These fields can only be used with getLong(TemporalField) because they return a number that is too large for an int. If you call now.get(JulianFields.MODIFIED_JULIAN_DAY) then an exception will be thrown: "UnsupportedTemporalTypeException: Invalid field ModifiedJulianDay for get() method, use getLong() instead"

请注意，JSR-310只能提供来自 TemporalField ，因此无法表示时间，数字全部基于午夜。计算也使用当地的午夜，而不是UTC，这应该被考虑在内。

Note that JSR-310 can only provide integral numbers from TemporalField, thus the time-of-day cannot be represented, and the numbers are all based on midnight. The calculations also use local midnight, not UTC, which should be taken into account.

这些字段也可以用于使用 Temporal ：

The fields can also be used to update a date/time object using a method on Temporal:

result = input.with(JulianFields.MODIFIED_JULIAN_DAY, 56685);