I am trying to convert 19 digit Unix timestamp such as 1558439504711000000
(one and a half quintillion) into a readable date/time format. My timestamp ends with 6 z
I think there is nothing wrong with that, you are dealing with a timestamp that represent a date in the FUTURE (a really far away date in the future).
If you consider this:
String timeStamp = "1558439504";
this should give you: 05/21/2019 @ 11:51am (UTC)
Then there is I think an easy way to get the Date. Just create the Instant first based on that timestamp and then do:
Date myDate = Date.from(instant);