iPROFS Technology Blog

Introduction.

We all know that working with dates in the Java language isn’t perfect, at least when you just look at the standard JDK. Not only is more then half of them methods in java.util.Date deprecated, but in order to get the Date of a java.util.Calendar you have to use the getTime() method. So when the base object aren’t that well to start with, things can only get worse when you start to mix in more technologies like XML.

When you are getting started with marshalling and unmarshalling java objects to XML you’re bound to run into the javax.xml.datatype.XMLGregorianCalendar. Did you ever try to get the Date value for a field unmarshalled from XML and wrote the following code:

Date date = xmlGregorianCalendar.toGregorianCalendar.getTime();

Why isn’t an XMLGregorianCalendar a GregorianCalendar just like a ArrayList is a List or a HashMap is a Map?

Oke, some smart people discovered these problems as well and started to specify a new Date and Time API (JSR 310).
Their idea are great although an anwser in the original JSR does give me some worries:

2.11 Are there any internationalization or localization issues?
No issues are expected.

In my opinion internationalization and localization are the major issues when working with dates and times, but hey, that’s propably just me.

So the expert group started on 13 februari 2007 and finished the early review on 28 march 2010.
I’m really wondering in which version of the JDK this well be included.
And of course once this has been introducted into the JDK: How long will it take to get it supported as the default datatype for  XML dates?

Solution.

Fortunately there is already a solution available: Joda-Time.
With it’s DateTime, Period, Interval and Duration objects it provided a mature, easy to use and comprehensive feature set.

There is only one slight problem: JAXB doesn’t know anything about Joda-Time and it’s DateTime object.
By default fields in an XML-file with a xsd:datetime type will be unmarshalled to an XMLGregorianCalendar.

In various projects I have seen DateConverter utility classes for conversion from and to the Joda-Time DateTime object.
Wouldn’t it be nice if you just could use the DateTime field and have the conversion be done as some form of ‘custom marshalling‘?
But wait: you can! The JAXB API specifies an XMLAdapter, which “Adapts a Java type for custom marshaling“

What we need is an XMLAdapter, which allows us marshal and unmashal between a ValueType and the BoundType.
The ValueType is some class, which JAXB knows how to handle out of the box (Strings, Lists or an Calendar and the BoundType is some type that JAXB doesn’t know how to handle. The Adapter will specify how transform from one type to the other.

So I’ve written a DateTimeAdapter, which unmashals from a Calender to DateTime and marshals a DateTime to a Calendar.

public class DateTimeAdapter extends XmlAdapter {

	@Override
	public DateTime unmarshal(Calendar calendar) throws Exception {
		return new DateTime(
			calendar.get(Calendar.YEAR),
			// Correct for the difference between Joda DateTime
			// and JDK Calendar.
			calendar.get(Calendar.MONTH) + 1,
			calendar.get(Calendar.DATE),
			calendar.get(Calendar.HOUR_OF_DAY),
			calendar.get(Calendar.MINUTE),
			calendar.get(Calendar.SECOND),
			calendar.get(Calendar.MILLISECOND),
			DateTimeZone.forTimeZone(calendar.getTimeZone()));
	}

	@Override
	public Calendar marshal(DateTime v) throws Exception {
		Calendar calendar = Calendar.getInstance(v.getZone().toTimeZone());
		calendar.setTime(v.toDate());
		return calendar;
	}

}

Now the tricky part: You have to tell the XML (un)marshaller that it should use the custom adapter for mashalling certain fields in your objects.
But as you propably could have guessed: the JAXB-API provides a solution for that as well:
Just add an XmlJavaTypeAdapter annotation to the field in your object and the Marshaller and Unmarshaller will invoke the Adapter during the process.

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "book", propOrder = {
    "author",
    "title",
    "publicationDate"
})
public class Book {

    @XmlElement(required = true)
    protected String author;
    @XmlElement(required = true)
    protected String title;
    @XmlElement(required = true)
    @XmlSchemaType(name = "date")
    @XmlJavaTypeAdapter(nl.iprofs.util.jaxb.adapter.DateTimeAdapter.class)
    private DateTime publicationDate;

    // Getters and Setters
    .....

}

Part 2: WsImport, Maven and XJC.

In the next blog about this topic I’ll dig into the topic of WsImport with Maven and XJC (XML to Java Compiler) which is being using in generating classes for webservices based upon a WSDL and Schema. If some generator is going to generate the java classes for the SOAP service, I want it to generate fields as DateTime objects and annotate them with my XMLAdapter.
Sound easy, but of course it isn’t just that.