getMilliseconds() out of Java Date
-
13-10-2019 - |
문제
I need a function like long getMillis(Date aDate);
that returns the milliseconds of the Date second. I cannot use Yoda, SimpleDateFormat or other libraries because it's gwt code.
My current solution is doing date.getTime() % 1000
Is there a better way?
해결책
As pointed by Peter Lawrey, in general you need something like
int n = (int) (date.getTime() % 1000);
return n<0 ? n+1000 : n;
since %
works in a "strange" way in Java. I call it strange, as I always need the result to fall into a given range (here: 0..999), rather than sometimes getting negative results. Unfortunately, it works this way in most CPUs and most languages, so we have to live with it.
다른 팁
Tried above and got unexpected behavior until I used the mod with 1000 as a long.
int n = (int) (date.getTime() % 1000l);
return n<0 ? n+1000 : n;
tl;dr
aDate.toInstant()
.toEpochMilli()
java.time
The modern approach uses java.time classes. These supplant the troublesome old legacy classes such as java.util.Date
.
Instant instant = Instant.now(); // Capture current moment in UTC.
Extract your count of milliseconds since epoch of 1970-01-01T00:00:00Z
.
long millis = instant.toEpochMilli() ;
Converting
If you are passed a java.util.Date
object, convert to java.time. Call new methods added to the old classes.
Instant instant = myJavaUtilDate.toInstant() ;
long millis = instant.toEpochMilli() ;