Convert between LocalDate and XMLGregorianCalendar

Converting from LocalDate to XMLGregorianCalendar:

LocalDate date = LocalDate.now();
GregorianCalendar gcal = GregorianCalendar.from(date.atStartOfDay(ZoneId.systemDefault()));
XMLGregorianCalendar xcal = DatatypeFactory.newInstance().newXMLGregorianCalendar(gcal);

Converting back is simpler:

xcal.toGregorianCalendar().toZonedDateTime().toLocalDate();