Java 8: Convert file time (milliseconds from 1970) to RFC 1123 format

Question

This seems like it should be simple, but so far nothing I try is working. Basically I want to convert a file time in milliseconds from 1970 (the usual) to a TemporalAccessor

Answer 1

The conversion to Instant succeeds without problem. The problem is the formatter. Use ISO_INSTANT formatter instead of RFC_1123_DATE_TIME then you should go:

        inst = Instant.now();
        System.out.println(java.time.format.DateTimeFormatter.ISO_INSTANT
                           .format( inst ) );

--> 2015-07-20T21:11:53.001Z

If you really want to have RFC_1123 format, you have to declare a timezone.

Either append it to the formatter :

        System.out.println(java.time.format.DateTimeFormatter.RFC_1123_DATE_TIME
                           .withZone( ZoneOffset.UTC )
                           .format( inst ) );

or convert the Instant to a ZonedDateTime:

        ZonedDateTime zdt = ZonedDateTime.ofInstant( inst, ZoneOffset.UTC );
        System.out.println(java.time.format.DateTimeFormatter.RFC_1123_DATE_TIME
                           .format( zdt ) );

--> Mon, 20 Jul 2015 21:11:53 GMT