More JAXB quirks

Today I ran across yet more quirks of JAXB 2.0. I'm getting really tired of running across stupid errors that are difficult to debug because the programmers who wrote JAXB are lazy. Today, I was receiving a java.lang.InternalError when I tried to compile a schema from beans I'd recently refactored. The error I received was something along the lines of "could not escape schema namespace". As it turns out, it was caused by the lack of an @XmlType annotation on the enums I had added to one of my XML serializable beans. I hope this helps anybody who has the same problem.

A quick note about JAXB

JAXB (the Java API for XML Binding) is a great piece of technology (2.x, not 1.x). However, if you're starting an application and your JAXBContext is throwing an exception saying that it's unaware of a given class, there's a quick fix. At this point, I'm guessing you've configured your JAXB context to use a package, and the class that the JAXBContext is unaware of is in the given package, and you're scratching your head as to why it can't seem to find a class that's in the proper package. Well, here's the most probable answer : if you're using package-configured JAXBContexts, you need to have factory methods for all top level elements, similar to the following :

    /**
     * Create an instance of {@link PurchaseOrder }
     * 
     */
    public PurchaseOrder createPurchaseOrder() {
        return new PurchaseOrder();
    }

... assuming that mypackage.PurchaseOrder is the class the JAXBContext is complaining that it's unaware of. This little quirk took me a couple hours to debug because I had just regenerated some web services code using Apache CXF 2.1.1 from an updated WSDL document for an updated Web Service that our company uses. Little did I know, that in comparing the two ObjectFactory files in Eclipse, I had missed copying over certain important functions. Hopefully this helps you.

RESTful web services with JAXB 2.0

In case you're not familiar, JAXB (Java API for Xml Binding) is an API developed by Sun for binding between XML and Java beans. The first incarnation, 1.x, was interface+implementation based like XMLBeans from the Apache Project. The second incarnation, 2.x, is annotation+pojo based. It's a very useful API, especially when combining it with Hibernate (and the Java Persistence API) to make restful web services. But, that's not really the point of this post. The point is that I've been using JAXB 2.0 for web services much in the past, but this is the first time where I've had to map the "class hierarchy per-table" pattern used by Hibernate into XML. As it turns out, JAXB 2 has very good support for this pattern. You can read more on this at the java.net project page for JAXB.