code: public static String convertTz(String dateStr, String format, String tzFrom, String tzTo) {
  		return dateFormatTz(toTimestampTz(dateStr, format, tzFrom), tzTo);
  	}
docs: Convert datetime string from a time zone to another time zone.
  @param dateStr the date time string
  @param format the date time format
  @param tzFrom the original time zone
  @param tzTo the target time zone