What is the Zone Id for GMT in Java 8 - java-8

Question

I want to get the difference in seconds to find whether the system timezone is ahead or behind the remote timezone. Here the remote timezone value is "GMT" which i fetch from Database. It could be "US/Eastern", which i convert to "America/New_York". But for GMT, im getting ERROR.
ZoneId.systemDefault().getRules().getOffset(Instant.now()).getTotalSeconds()
- ZoneId.of("GMT").getRules().getOffset(Instant.now()).getTotalSeconds()
But it gives the following error,
Exception in thread "main" java.time.DateTimeException: Invalid ID for ZoneOffset, invalid format:
at java.time.ZoneOffset.of(Unknown Source)
at java.time.ZoneId.of(Unknown Source)
at java.time.ZoneId.of(Unknown Source)
How to resolve this error ?
What to use in place of GMT ??

Answer 1

Use Etc/UTC
import java.time.Instant;
import java.time.ZoneId;
public class Main {
public static void main(String args[]) {
System.out.println(ZoneId.of("Etc/UTC").getRules().getOffset(Instant.now()).getTotalSeconds());
}
}
Output:
0

Answer 2

The official answer is:
Etc/GMT
It’s the same as the Etc/UTC suggested in the other answers except for the name.
For the sake of completeness there are a number of aliases for the same, many of them deprecated, not all. You can find them in the link.
And I am not disagreeing with the comments telling you to prefer UTC. I just wanted to answer the question as asked.
For your case you should not need to ask at all though. ZoneId.of("GMT").getRules().getOffset(Instant.now()).getTotalSeconds() should always yield 0, so there is no need to subtract anything. I would either insert a comment why I don’t or subtract a well-named constant with the value 0.
Link: List of tz database time zones

Answer 3

It's ZoneId.of("UTC")...
Here's evidence:
public static void main(String[] args) {
// define the ZoneId
ZoneId utc = ZoneId.of("UTC");
// get the current date and time using that zone
ZonedDateTime utcNow = ZonedDateTime.now(utc);
// define a formatter that uses O for GMT in the output
DateTimeFormatter gmtStyleFormatter = DateTimeFormatter
.ofPattern("uuuu-MM-dd'T'HH:mm:ss.SSS O");
// and print the datetime using the default DateTimeFormatter and the one defined above
System.out.println(utcNow + " == " + utcNow.format(gmtStyleFormatter));
}
output (some moments ago):
2020-09-16T08:02:34.717Z[UTC] == 2020-09-16T08:02:34.717 GMT
Getting the total zone offset in seconds of this zone by
utc.getRules().getOffset(Instant.now()).getTotalSeconds();
will result in 0, because this zone has no offset.