转换到格林威治标准时间

public static Date getGreenwichTime(Date date) 
{
	TimeZone tzGreenwich = TimeZone.getTimeZone(TIME_ZONE_GREENWICH);

	// convert time to Greenwich
	Calendar cal = Calendar.getInstance();
	cal.setTimeInMillis(date.getTime() - tzGreenwich.getOffset(date.getTime()));

	return cal.getTime();
}