You are using an Instant to get that milliseconds representation. Instant are not zone based. Now, the epoch time is based on the “1970-01-01T00:00:00Z” so you should not have the zone in it.
If you want to create a ZoneDateTime from the epoch value, you can simply create an Instant at that epoch time and then create a ZonedDateTime with the zone you wish :
//Let's create our zone time (just to keep your logic
LocalDateTime ldt = LocalDateTime.now();
ZonedDateTime zonedDateTime =ldt.atZone(ZoneId.of("Asia/Kolkata"));
//Then get the epoch on GMT
long e = zonedDateTime.toInstant().toEpochMilli();
Instant i = Instant.ofEpochMilli(e);
System.out.println(ZonedDateTime.ofInstant(i, ZoneId.systemDefault()));
System.out.println(ZonedDateTime.ofInstant(i, ZoneId.of("Asia/Kolkata")));
2019-04-12T05:10:31.016+02:00[Europe/Paris]
2019-04-12T08:40:31.016+05:30[Asia/Kolkata]
NOTE : The code above should not be used like this, it is not necessary to get a LocalDateTime then a ZonedDateTime to finally create an Instant. This is just to show that even with a zone, this will be “lost” at one point.
Simply use :
long e = Instant.now().toEpochMilli();