How to get milliseconds from LocalDateTime in Java 8
JavaDatetimeJava 8MillisecondsJava TimeJava Problem Overview
I am wondering if there is a way to get current milliseconds since 1-1-1970 (epoch) using the new LocalDate
, LocalTime
or LocalDateTime
classes of Java 8.
The known way is below:
long currentMilliseconds = new Date().getTime();
or
long currentMilliseconds = System.currentTimeMillis();
Java Solutions
Solution 1 - Java
I'm not entirely sure what you mean by "current milliseconds" but I'll assume it's the number of milliseconds since the "epoch," namely midnight, January 1, 1970 UTC.
If you want to find the number of milliseconds since the epoch right now, then use System.currentTimeMillis()
as Anubian Noob has pointed out. If so, there's no reason to use any of the new java.time APIs to do this.
However, maybe you already have a LocalDateTime
or similar object from somewhere and you want to convert it to milliseconds since the epoch. It's not possible to do that directly, since the LocalDateTime
family of objects has no notion of what time zone they're in. Thus time zone information needs to be supplied to find the time relative to the epoch, which is in UTC.
Suppose you have a LocalDateTime
like this:
LocalDateTime ldt = LocalDateTime.of(2014, 5, 29, 18, 41, 16);
You need to apply the time zone information, giving a ZonedDateTime
. I'm in the same time zone as Los Angeles, so I'd do something like this:
ZonedDateTime zdt = ldt.atZone(ZoneId.of("America/Los_Angeles"));
Of course, this makes assumptions about the time zone. And there are edge cases that can occur, for example, if the local time happens to name a time near the Daylight Saving Time (Summer Time) transition. Let's set these aside, but you should be aware that these cases exist.
Anyway, if you can get a valid ZonedDateTime
, you can convert this to the number of milliseconds since the epoch, like so:
long millis = zdt.toInstant().toEpochMilli();
Solution 2 - Java
What I do so I don't specify a time zone is,
System.out.println("ldt " + LocalDateTime.now().atZone(ZoneId.systemDefault()).toInstant().toEpochMilli());
System.out.println("ctm " + System.currentTimeMillis());
gives
ldt 1424812121078
ctm 1424812121281
As you can see the numbers are the same except for a small execution time.
Just in case you don't like System.currentTimeMillis, use Instant.now().toEpochMilli()
Solution 3 - Java
Since Java 8 you can call java.time.Instant.toEpochMilli()
.
For example the call
final long currentTimeJava8 = Instant.now().toEpochMilli();
gives you the same results as
final long currentTimeJava1 = System.currentTimeMillis();
Solution 4 - Java
To avoid ZoneId you can do:
LocalDateTime date = LocalDateTime.of(1970, 1, 1, 0, 0);
System.out.println("Initial Epoch (TimeInMillis): " + date.toInstant(ZoneOffset.ofTotalSeconds(0)).toEpochMilli());
Getting 0 as value, that's right!
Solution 5 - Java
You can use java.sql.Timestamp
also to get milliseconds.
LocalDateTime now = LocalDateTime.now();
long milliSeconds = Timestamp.valueOf(now).getTime();
System.out.println("MilliSeconds: "+milliSeconds);
Solution 6 - Java
To get the current time in milliseconds (since the epoch), use System.currentTimeMillis()
.
Solution 7 - Java
You can try this:
long diff = LocalDateTime.now().atZone(ZoneOffset.UTC).toInstant().toEpochMilli();
Solution 8 - Java
Why didn't anyone mentioned the method LocalDateTime.toEpochSecond()
:
LocalDateTime localDateTime = ... // whatever e.g. LocalDateTime.now()
long time2epoch = localDateTime.toEpochSecond(ZoneOffset.UTC);
This seems way shorter that many suggested answers above...
Solution 9 - Java
If you have a Java 8 Clock, then you can use clock.millis()
(although it recommends you use clock.instant()
to get a Java 8 Instant, as it's more accurate).
Why would you use a Java 8 clock? So in your DI framework you can create a Clock bean:
@Bean
public Clock getClock() {
return Clock.systemUTC();
}
and then in your tests you can easily Mock it:
@MockBean private Clock clock;
or you can have a different bean:
@Bean
public Clock getClock() {
return Clock.fixed(instant, zone);
}
which helps with tests that assert dates and times immeasurably.
Solution 10 - Java
Date and time as String to Long (millis):
String dateTimeString = "2020-12-12T14:34:18.000Z";
DateTimeFormatter formatter = DateTimeFormatter
.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'", Locale.ENGLISH);
LocalDateTime localDateTime = LocalDateTime
.parse(dateTimeString, formatter);
Long dateTimeMillis = localDateTime
.atZone(ZoneId.systemDefault())
.toInstant()
.toEpochMilli();
Solution 11 - Java
default LocalDateTime getDateFromLong(long timestamp) {
try {
return LocalDateTime.ofInstant(Instant.ofEpochMilli(timestamp), ZoneOffset.UTC);
} catch (DateTimeException tdException) {
// throw new
}
}
default Long getLongFromDateTime(LocalDateTime dateTime) {
return dateTime.atOffset(ZoneOffset.UTC).toInstant().toEpochMilli();
}
Solution 12 - Java
I think this is more simpler:
ZonedDateTime zdt = ZonedDateTime.of(LocalDateTime.now(), ZoneId.systemDefault());
Assert.assertEquals(System.currentTimeMillis(), zdt.toInstant().toEpochMilli());
get the millis like System.currentTimeMillis() (from UTC).
Solution 13 - Java
For LocalDateTime I do it this way:
LocalDateTime.of(2021,3,18,7,17,24,341000000)
.toInstant(OffsetDateTime.now().getOffset())
.toEpochMilli()
Solution 14 - Java
There are some methods available that no one has mentioned here. But I don't see a reason why they should not work.
In case of LocalDate
, you can use the toEpochDay()
method. It returns the number of days since 01/01/1970. That number then can be easily converted to milliseconds:
long dateInMillis = TimeUnit.DAYS.toMillis(myLocalDate.toEpochDays());
Documentation can be found here.
In case of LocalDateTime
, you can use the toEpochSecond()
method. It returns the number of seconds since 01/01/1970. That number then can be converted to milliseconds, too:
long dateTimeInMillis = TimeUnit.SECONDS.toMillis(myLocalDateTime.toEpochSeconds());
Documentation for that is here.