My xmlGregorianCalendar coming with offset value ..how to adjust it? in java

Question

My xmlGregorianCalendar value coming as 2020-10-02T13:07:38-06:00 .. I want to pass thisxmlGregorianCalendar value and get the output like 2020-10-02T07:07:38(which reduces 6 hours from the time) any suggestion on this please?

I have used this below method.

return new Timestamp(xmlGregorianCalendar.toGregorianCalendar(TimeZone.getTimeZone("GMT"),null,null).getTimeInMillis())..

But it removing the off set value but not adjusting the time. the output i am getting is 2020-10-02T13:07:38..But i am expecting the 2020-10-02T07:07:38 like this.

Answer 1

First of all, I recommend you switch from the outdated and error-prone java.util date-time API to the modern java.time date-time API. Learn more about the modern date-time API from Trail: Date Time.

Your understanding of Zone-Offset is not correct

The date-time string, 2020-10-02T13:07:38-06:00 tells us that the given date and time has been adjusted with an offset of -06:00 hours from UTC i.e. the corresponding date-time at UTC would be 2020-10-02T19:07:38Z where Z specifies a Zone-Offset of 00:00 hours.

It means that if you are expecting a date-time of 2020-10-02T07:07:38, you need to offset the given date-time further by -06:00 hours i.e. it will be at a total of -12:00 hours offset from UTC.

The following example illustrates this concept:

import java.time.OffsetDateTime;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;

public class Main {
    public static void main(String[] args) {
        OffsetDateTime odtGiven = OffsetDateTime.parse("2020-10-02T13:07:38-06:00");
        System.out.println(odtGiven);

        // Date and time at Zone-Offset of 00:00 hours
        OffsetDateTime odtUTC = odtGiven.withOffsetSameInstant(ZoneOffset.UTC);
        System.out.println(odtUTC);

        // Date and time at Zone-Offset of -12:00 hours
        OffsetDateTime odtDerived = odtGiven.withOffsetSameInstant(ZoneOffset.of("-12:00"));
        System.out.println(odtDerived);

        // Get the date-time string in the format with Zone-Offset dropped
        String strDateTimeZoneOffsetDropped = odtDerived.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME);
        System.out.println(strDateTimeZoneOffsetDropped);
    }
}

Output:

2020-10-02T13:07:38-06:00
2020-10-02T19:07:38Z
2020-10-02T07:07:38-12:00
2020-10-02T07:07:38

Using the legacy API:

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

import javax.xml.datatype.DatatypeConfigurationException;
import javax.xml.datatype.DatatypeFactory;
import javax.xml.datatype.XMLGregorianCalendar;

public class Main {
    public static void main(String[] args) throws DatatypeConfigurationException, ParseException {
        String givenDateTimeString = "2020-10-02T13:07:38-06:00";
        XMLGregorianCalendar xmlGregorianCalendar = DatatypeFactory.newInstance()
                .newXMLGregorianCalendar(givenDateTimeString);
        System.out.println(xmlGregorianCalendar);

        // Derive the date-time string at Zone-Offset of UTC-12:00 hours
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
        sdf.setTimeZone(TimeZone.getTimeZone("GMT-12:00"));
        Date date = xmlGregorianCalendar.toGregorianCalendar().getTime();
        String derivedDateTimeString = sdf.format(date);
        System.out.println(derivedDateTimeString);
    }
}

Output:

2020-10-02T13:07:38-06:00
2020-10-02T07:07:38

Answer 2

JDBC 4.2 and java.time

Arvind Kumar Avinash has already nicely explained how the offset works (what XMLGregorianCalendar misleadingly calls a time zone). He has also already recommended java.time, the modern Java date and time API. I should like to elaborate on this recommendation. Assuming that you thought you wanted a java.sql.Timestamp for your SQL database, you should not want that. Since JDBC 4.2 and Hibernate 5 we can seamlessly transfer the types of java.time to our SQL databases. Which I recommend that you do instead.

If using timestamp with time zone in SQL, use OffsetDateTime in UTC in Java

If the datatype in SQL is timestamp with time zone (recommended for timestamps), transfer an OffsetDateTime from Java to it. To most database engines timestamp with time zone really means timestamp in UTC, so for clarity I prefer to pass an OffsetDateTime that is in UTC too. There are a couple of ways to convert, each with their pros and cons.

1. Convert via GregorianCalendar.

    // For demonstration build an XMLGregorianCalenadr equivalent to yours
    XMLGregorianCalendar xmlGregorianCalendar = DatatypeFactory.newInstance()
            .newXMLGregorianCalendar("2020-10-02T13:07:38-06:00");
    
    // Convert to OffsetDateTime for your SQL database
    OffsetDateTime dateTime = xmlGregorianCalendar.toGregorianCalendar()
            .toZonedDateTime()
            .toOffsetDateTime()
            .withOffsetSameInstant(ZoneOffset.UTC);

    // Show what we’ve got
    System.out.println(dateTime);

Output is:

2020-10-02T19:07:38Z

Pro: it’s the official conversion.

Or 2. Convert via String.

    OffsetDateTime dateTime = OffsetDateTime.parse(xmlGregorianCalendar.toString())
            .withOffsetSameInstant(ZoneOffset.UTC);

Pro: it’s short, and I don’t think it gives any surprises. Con: To me it feels like a waste to format into a string and parse back into a date-time object again.

3. Convert via int. You may convert by taking the individual fields out of the XMLGregorianCalendar and building an OffsetDateTime from them. It’s getting long-winded, handling fraction of second is a bit complicated, and there’s a risk of accidentally swapping fields, so I don’t recommend it.

How to pass to SQL. Here’s an example of transferring the OffsetDateTime to SQL.

    String sqlString = "insert into your_table(your_timestamp_column) values (?);";
    PreparedStatement ps = yourDatabaseConnection.prepareStatement(sqlString);
    ps.setObject(1, dateTime);
    int rowsInserted = ps.executeUpdate();

If using timestamp without time zone in SQL, instead pass a LocalDateTime from Java

If the datatype in SQL is timestamp without time zone (not recommended for timestamps, but often seen), you need to pass a LocalDateTime from Java. Again there are a couple of ways to convert. I am showing just one:

    LocalDateTime dateTime = xmlGregorianCalendar.toGregorianCalendar()
            .toZonedDateTime()
            .withZoneSameInstant(ZoneId.systemDefault())
            .toLocalDateTime();

I am using the default time zone of the JVM in agreement with what the old-fashioned Timestamp class did, so the result is time zone dependent. In my time zone (Europe/Copenhagen) currently at UTC offset +02:00, the result is:

2020-10-02T21:07:38

What went wrong in your code?

The three-arg XMLGregorianCalendar.toGregorianCalendar​(TimeZone, Locale, XMLGregorianCalendar) that you were using is designed to introduce bugs like the one you observed. It promises to construct a GregorianCalendar with the specified time zone (if one is given) and with the field values from the XMLGregorianCalendar (year, month, day, hour, minute, etc.). So the documentation says it quite clearly: if you specify a time zone that does not agree with the offset of the XMLGregorianCalendar, it gives you a different point in time than the one specified by the XMLGregorianCalendar. It might occasionally be useful if the XMLGregorianCalendar hadn’t got any offset and we knew which time zone was intended. But your XMLGregorianCalendar has got offset, so this method definitely is not what you want to use.

Links

• Oracle tutorial: Date Time explaining how to use java.time.
• Documentation of the three-arg XMLGregorianCalendar.toGregorianCalendar​(TimeZone, Locale, XMLGregorianCalendar)