Simple conversion between java.util.Date and XMLGregorianCalendar

Question

I'm looking for a simple method of converting between java.util.Date and javax.xml.datatype.XMLGregorianCalendar in both directions.

Here is the code that I'm using now:

import java.util.GregorianCalendar;
import javax.xml.datatype.DatatypeConfigurationException;
import javax.xml.datatype.DatatypeFactory;
import javax.xml.datatype.XMLGregorianCalendar;

/**
 * Utility class for converting between XMLGregorianCalendar and java.util.Date
 */
public class XMLGregorianCalendarConverter {  

    /**
     * Needed to create XMLGregorianCalendar instances
     */
    private static DatatypeFactory df = null;
    static {
        try {
            df = DatatypeFactory.newInstance();
        } catch (DatatypeConfigurationException dce) {
            throw new IllegalStateException(
                "Exception while obtaining DatatypeFactory instance", dce);
        }
    }  

    /**
     * Converts a java.util.Date into an instance of XMLGregorianCalendar
     *
     * @param date Instance of java.util.Date or a null reference
     * @return XMLGregorianCalendar instance whose value is based upon the
     *  value in the date parameter. If the date parameter is null then
     *  this method will simply return null.
     */
    public static XMLGregorianCalendar asXMLGregorianCalendar(java.util.Date date) {
        if (date == null) {
            return null;
        } else {
            GregorianCalendar gc = new GregorianCalendar();
            gc.setTimeInMillis(date.getTime());
            return df.newXMLGregorianCalendar(gc);
        }
    }

    /**
     * Converts an XMLGregorianCalendar to an instance of java.util.Date
     *
     * @param xgc Instance of XMLGregorianCalendar or a null reference
     * @return java.util.Date instance whose value is based upon the
     *  value in the xgc parameter. If the xgc parameter is null then
     *  this method will simply return null.
     */
    public static java.util.Date asDate(XMLGregorianCalendar xgc) {
        if (xgc == null) {
            return null;
        } else {
            return xgc.toGregorianCalendar().getTime();
        }
    }
}

Is there anything simpler, like some API call that I have overlooked?

Converting between a standard XML date/time and a Java date object seems like a pretty routine task and I'm surprised that I have to write this code at all.

Any suggestions?

NOTES: My JAXB classes are autogenerated from a schema. The build process on my project does not allow for me to make manual changes to the generated classes. The xs:dateTime elements are being generated by XJC as XMLGregorianCalendar in the JAXB classes. The schema is extended and tweaked periodically, so I am allowed to make limited changes to the schema XSD file.

UPDATE ON SOLUTION: The solution proposed by Blaise has allowed me to take XMLGregorianCalendar out of the mix and deal with java.util.Calendar objects instead. By adding a JAXB binding clause at the top of my schema file, XJC is able to generate more appropriate mappings for xs:dateTime in my JAXB classes. Here are some snippets that show the modifications in my XSD file.

The root element in the XSD file:

<xs:schema xmlns:mydata="http://my.example.com/mydata" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:jaxb="http://java.sun.com/xml/ns/jaxb" targetNamespace="http://my.example.com/mydata" elementFormDefault="unqualified" attributeFormDefault="unqualified" version="0.2" xml:lang="en" jaxb:version="2.0">

JAXB binding annotation block, inserted immediately after root element in XSD:

<xs:annotation>
    <xs:appinfo>
        <jaxb:globalBindings>
            <jaxb:javaType name="java.util.Calendar" xmlType="xs:dateTime" parseMethod="javax.xml.bind.DatatypeConverter.parseDateTime" printMethod="javax.xml.bind.DatatypeConverter.printDateTime" />
        </jaxb:globalBindings>
    </xs:appinfo>
</xs:annotation>

Since the XML xs:dateTime field also stores timezone, it might be better for me to work with Calendar instead of Date anyway since Calendar objects have a pretty good API for working with locales and timezones. In any case, I'm much happier to deal with Calendar objects instead of XMLGregorianCalendar. No need for the conversion methods that I listed above anymore. I didn't get all the way to java.util.Date, but close enough!

Answer 1

From XMLGregorianCalendar to java.util.Date you can simply do:

java.util.Date dt = xmlGregorianCalendarInstance.toGregorianCalendar().getTime();