问题
I'm trying to get the total amount of Milliseconds (not the millis field) from the Period object instance. I've tried multiple conversions, as I couldn't find any method easily giving it.
Has anyone ever needed that and managed to retrieve it ?
(I need this for my patch, to figure out a negative period; negative millis = negative period.)
回答1:
You can't get the millis directly from a Period, since fields like months and years are variable in terms of milliseconds.
In order to make this work, you need to supply a "baseline" instant from which Period can calculate that actual millisecond duration.
For example, the Period.toDurationFrom and Period.toDurationTo methods take such a baseline instant, and calculate a Duration object, which you can then obtain the millis.
The Javadoc for toDurationFrom says:
Gets the total millisecond duration of this period relative to a start instant. This method adds the period to the specified instant in order to calculate the duration.
An instant must be supplied as the duration of a period varies. For example, a period of 1 month could vary between the equivalent of 28 and 31 days in milliseconds due to different length months. Similarly, a day can vary at Daylight Savings cutover, typically between 23 and 25 hours.
So you need to pick an appropriate baseline instant for your application.
回答2:
If you want to get the millis from a specific time it can be done by using the plus() or minus() methods of the DateTime class.
e.g. getting the millis from now
DateTime start = new DateTime(); //NOW
DateTime end = start.plus(<your period>);
long millis = end.getMillis() - start.getMillis();
回答3:
Using Joda time 2.3, it is:
toStandardDuration().getMillis()
来源：https://stackoverflow.com/questions/9625306/joda-time-period-to-total-millis