Java: Calculating time zone difference

Question

How do I get the time difference from GMT for a specific date and time zone in Java?

Determining whether a specific time zone is in DST is quite straight-forward:

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Answer 1

public String timeZone(Date date) {
    TimeZone timeZone = TimeZone.getTimeZone("America/New_York");
    long millis = timeZone.getRawOffset() + (timeZone.inDaylightTime(date) ? timeZone.getDSTSavings() : 0);

    return String.format("%s%s:%s",
            millis < 0 ? "-" : "+",
            String.format("%02d", Math.abs(TimeUnit.MILLISECONDS.toHours(millis))),
            String.format("%02d", Math.abs(TimeUnit.MILLISECONDS.toMinutes(millis) - TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(millis))))
    );
}