- * Converts a {@link ZonedDateTime} to a {@link GregorianCalendar}, as suggested
- * in the official Java 8 Time tutorial.
- * <p>
- * The {@link GregorianCalendar} can then be persisted as
- * {@link java.persistene.TemporalType.TIMESTAMP} with the help of the
- * {@link java.persist.Tmporal}-annotation.
- * @see https://docs.oracle.com/javase/tutorial/datetime/iso/legacy.html