Local to UTC time zone conversion with tests

public interface DateConversionHelper {

	static LocalDateTime fromXmlDate(XMLGregorianCalendar calendar) {
		if (calendar == null) {
			return null;
		}
		final int year = calendar.getYear() > 0 ? calendar.getYear() : 0;
		final int month = calendar.getMonth();
		final int day = calendar.getDay();
		final int hour = calendar.getHour() > 0 ? calendar.getHour() : 0;
		final int minute = calendar.getMinute() > 0 ? calendar.getMinute() : 0;
		final int second = calendar.getSecond() > 0 ? calendar.getSecond() : 0;
		final int millisecond = calendar.getMillisecond() > 0 ? calendar.getMillisecond() : 0;

		final ZoneOffset offset = LocalDateTime.now().atZone(ZoneId.of("UTC")).withZoneSameLocal(ZoneId.systemDefault()).toOffsetDateTime().getOffset();
		return LocalDateTime.of(year, month, day, hour, minute, second, millisecond).plusSeconds(offset.getTotalSeconds());
	}

	static XMLGregorianCalendar toXmlDate(LocalDate value) {
		if (value == null) {
			return null;
		}
		try {
			GregorianCalendar calendar = new GregorianCalendar(TimeZone.getTimeZone("UTC"));
			calendar.setTime(value);
			return DatatypeFactory.newInstance().newXMLGregorianCalendar(calendar);
		} catch (DatatypeConfigurationException ex) {
			//WTF ENTERPRISE PIECE OF SHIT
			throw new RuntimeException(ex);
		}
	}

	static XMLGregorianCalendar toXmlDate(LocalDateTime value) {
		if (value == null) {
			return null;
		}
		try {
			GregorianCalendar calendar = new GregorianCalendar(TimeZone.getTimeZone("UTC"));
			calendar.setTime(value);
			return DatatypeFactory.newInstance().newXMLGregorianCalendar(calendar);
		} catch (DatatypeConfigurationException ex) {
			throw new RuntimeException(ex);
		}
	}

	static XMLGregorianCalendar toXmlDate(Date value) {
		if (value == null) {
			return null;
		}
		try {
			GregorianCalendar calendar = new GregorianCalendar(TimeZone.getTimeZone("UTC"));
			calendar.setTime(value);
			return DatatypeFactory.newInstance().newXMLGregorianCalendar(calendar);
		} catch (DatatypeConfigurationException ex) {
			throw new RuntimeException(ex);
		}
	}

}

public class DateConversionHelperTest {

	@Test
	public void shouldConvertUtcCalendarToLocalDateTime() throws Exception {
		GregorianCalendar calendar = new GregorianCalendar(TimeZone.getTimeZone("UTC"));
		calendar.setTime(new GregorianCalendar(2014, 0, 1, 0, 0, 0).getTime());
		final XMLGregorianCalendar xmlCalendar = DatatypeFactory.newInstance().newXMLGregorianCalendar(calendar);

		final LocalDateTime date = DateConversionHelper.fromXmlDate(xmlCalendar);
		assertEquals("2014-01-01T00:00", date.toString());
	}

	@Test
	public void shouldConvertDateTimeToUtcForm() throws Exception {
		final XMLGregorianCalendar calendar = DateConversionHelper.toXmlDate(LocalDateTime.of(2014, 1, 1, 0, 0, 0));
		assertEquals("2013-12-31T23:00:00.000Z", calendar.toString());
	}

	@Test
	public void shouldConvertDateToUtcForm() throws Exception {
		final XMLGregorianCalendar calendar = DateConversionHelper.toXmlDate(LocalDate.of(2014, 1, 1));
		assertEquals("2013-12-31T23:00:00.000Z", calendar.toString());
	}

	@Test
	public void shouldConvertOldDateToUtcForm() throws Exception {
		final XMLGregorianCalendar calendar = DateConversionHelper.toXmlDate(new GregorianCalendar(2014, 0, 1, 0, 0, 0).getTime());
		assertEquals("2013-12-31T23:00:00.000Z", calendar.toString());
	}

}