code: private XMLGregorianCalendar createCalendar(Long timestamp) throws Exception {
          DatatypeFactory df = DatatypeFactory.newInstance();
          GregorianCalendar cal = new GregorianCalendar();
          cal.setTimeInMillis(timestamp != null ? timestamp.longValue() : System.currentTimeMillis());
          return df.newXMLGregorianCalendar(cal);
      }
docs: Erzeugt ein Calendar-Objekt.
  
  @param timestamp der Zeitstempel.
  @return das Calendar-Objekt.
  @throws Exception