Since Groovy 1.8.3 we can use an extra TimeZone parameter with the format() method of the Date class. This can be used to print a date/time for a particular timezone.
import static java.util.Calendar.*
def timeZone = TimeZone.getTimeZone('Europe/Amsterdam')
def otherTimeZone = TimeZone.getTimeZone('Australia/Canberra')
def cal = Calendar.instance
cal.set(year: 2011, month: OCTOBER, date: 20, hourOfDay: 12, minute: 30)
def date = cal.time
def dateFormat = 'yyyy/MM/dd HH:mm'
assert date.format(dateFormat, timeZone) == '2011/10/20 12:30'
assert date.format(dateFormat, otherTimeZone) == '2011/10/20 21:30'
