XML GregorianCalendar 支持保存日期时间格式为YMD

       GregorianCalendar calendar = new GregorianCalendar();
        calendar.setTime(new Date());
        XMLGregorianCalendar gc = null;
        try {
            gc = DatatypeFactory.newInstance().newXMLGregorianCalendar(calendar);
    
            //保留年月日去掉时间后的格式
            gc.setTimezone(DatatypeConstants.FIELD_UNDEFINED);
            System.out.println("去掉时间后的格式:"+gc.toString());
    
            gc.setTime(DatatypeConstants.FIELD_UNDEFINED,
                    DatatypeConstants.FIELD_UNDEFINED,
                    DatatypeConstants.FIELD_UNDEFINED,
                    DatatypeConst