First of all, check the documentation of SimpleDateFormat
. The pattern that corresponds to milliseconds is an uppercase S
, while the lowercase s
corresponds to seconds. The problem is that SimpleDateFormat
usually doesn't complain and try to parse 423
as seconds, adding this amount to your end date (giving an incorrect result).
Anyway, SimpleDateFormat
just parses a String
to a java.util.Date
or formats the Date
to a String
. If you want the epoch millis value, you must get it from the Date
object:
// input string
String s = "2017.07.19 11:42:30:423";
// use correct format ('S' for milliseconds)
SimpleDateFormat formatter = new SimpleDateFormat("yyyy.MM.dd HH:mm:ss:SSS");
// parse to a date
Date date = formatter.parse(s);
// get epoch millis
long millis = date.getTime();
System.out.println(millis); // 1500475350423
The problem is that SimpleDateFormat
uses the system's default timezone, so the final value above (1500475350423
) will be equivalent to the specificed date and time in my system's timezone (which can be different from yours - just for the record, my system's default timezone is America/Sao_Paulo
). If you want to specify in what timezone this date is, you need to set in the formatter (before calling parse
):
// set a timezone to the formatter (using UTC as example)
formatter.setTimeZone(TimeZone.getTimeZone("UTC"));
With this, the result for millis
will be 1500464550423
(the equivalent to the specificed date and time in UTC).
To do the opposite (create a date from the millis value), you must create a Date
object and then pass it to the formatter (also taking care of setting a timezone to the formatter):
// create date from millis
Date date = new Date(1500464550423L);
// use correct format ('S' for milliseconds)
SimpleDateFormat formatter = new SimpleDateFormat("yyyy.MM.dd HH:mm:ss:SSS");
formatter.setTimeZone(TimeZone.getTimeZone("UTC"));
// format date
String formatted = formatter.format(date);
Java new date/time API
The old classes (Date
, Calendar
and SimpleDateFormat
) have lots of problems and design issues, and they're being replaced by the new APIs.
If you're using Java 8, consider using the new java.time API. It's easier, less bugged and less error-prone than the old APIs.
If you're using Java <= 7, you can use the ThreeTen Backport, a great backport for Java 8's new date/time classes. And for Android, there's the ThreeTenABP (more on how to use it here).
The code below works for both.
The only difference is the package names (in Java 8 is java.time
and in ThreeTen Backport (or Android's ThreeTenABP) is org.threeten.bp
), but the classes and methods names are the same.
As the input String
has no timezone information (only date and time), first I parsed it to a LocalDateTime
(a class that represents a date and time without timezone). Then I convert this date/time to a specific timezone and get the millis value from it:
// input string
String s = "2017.07.19 11:42:30:423";
// use correct format ('S' for milliseconds)
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy.MM.dd HH:mm:ss:SSS");
// as the input string has no timezone information, parse it to a LocalDateTime
LocalDateTime dt = LocalDateTime.parse(s, formatter);
// convert the LocalDateTime to a timezone
ZonedDateTime zdt = dt.atZone(ZoneId.of("Europe/London"));
// get the millis value
long millis = zdt.toInstant().toEpochMilli(); // 1500460950423
The value is now 1500460950423
, equivalent to the specified date and time in London timezone.
Note that the API uses IANA timezones names (always in the format Region/City
, like America/Sao_Paulo
or Europe/Berlin
).
Avoid using the 3-letter abbreviations (like CST
or PST
) because they are ambiguous and not standard.
You can get a list of available timezones (and choose the one that fits best your system) by calling ZoneId.getAvailableZoneIds()
.
You can also use ZoneOffset.UTC
constant if you want to use UTC.
To do the opposite, you can get the millis value to create an Instant, convert it to a timezone and pass it to the formatter:
// create Instant from millis value
Instant instant = Instant.ofEpochMilli(1500460950423L);
// use correct format ('S' for milliseconds)
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy.MM.dd HH:mm:ss:SSS");
// convert to timezone
ZonedDateTime z = instant.atZone(ZoneId.of("Europe/London"));
// format
String formatted = z.format(formatter);