Converting a time to milliseconds correctly in java.time (Java 8)

Question

I've been trying to convert a "DateTime" to milliseconds using the java.time package built into Java 8.

But I haven't been able to do it correctly. I am trying to convert "29/Jan/2015:18:00:00" to milliseconds. The following is something I tried

Instant instant = Instant.parse("2015-01-29T18:00:00.0z"); Long instantMilliSeconds = Long.parseLong(instant.getEpochSecond() + "" + instant.get(ChronoField.MILLI_OF_SECOND)); System.out.println(new Date(instantMilliSeconds)); // prints Sun Jun 14 05:06:00 PDT 1970 

I tried using LocalDateTime, but couldn't find a way to effectively do the conversion to milliseconds. I am not saying this is the best way to do this, if you know something better, I would really appreciate some pointers.

Answer 1

You should use Instant::toEpochMilli.

---

System.out.println(instant.toEpochMilli()); System.out.println(instant.getEpochSecond()); System.out.println(instant.get(ChronoField.MILLI_OF_SECOND)); 

prints

1422554400000 1422554400 0 

Your version did not work because you forgot to pad instant.get(ChronoField.MILLI_OF_SECOND) with extra zeros to fill it out to 3 places.

Answer 2

From Date and Time Classes the tutorials...

DateTimeFormatter formatter                     = DateTimeFormatter.ofPattern("dd/MMM/yyyy:HH:mm:ss"); LocalDateTime date = LocalDateTime.parse("29/Jan/2015:18:00:00", formatter); System.out.printf("%s%n", date); 

Prints 2015-01-29T18:00

ZoneId id = ZoneId.systemDefault(); ZonedDateTime zdt = ZonedDateTime.of(date, id); System.out.println(zdt.toInstant().toEpochMilli()); 

Prints 1422514800000