code: public static int getTimezoneOffsetInMinutes (@Nonnull final Calendar aCalendar)
    {
      final int nOffsetInMillis = aCalendar.getTimeZone ().getOffset (aCalendar.getTimeInMillis ());
      return getTimezoneOffsetInMinutes (nOffsetInMillis);
    }
docs: Get the time zone offset to UTC of the passed calendar in minutes to be
  used in {@link XMLGregorianCalendar}.
  
  @param aCalendar
  The calendar to use. May not be <code>null</code>.
  @return 0 for no offset to UTC, the minutes otherwise. Usually in 60minutes
  steps :)