when does JAXB unmarshaller.unmarshal returns a JAXBElement<MySchemaObject> or a MySchemaObject?

Question

I have two codes, in two different java projects, doing almost the same thing, (unmarshalling the input of a webservice according to an xsd-file).

But in one case I should write this: (Input is a placeholder name) ( element is OMElement input )

ClassLoader clInput = input.ObjectFactory.class.getClassLoader(); JAXBContext jc = JAXBContext.newInstance("input", clInput); Unmarshaller unmarshaller = jc.createUnmarshaller(); Input input = (Input)unmarshaller.unmarshal( element.getXMLStreamReader() ); 

and in the other lib I must use JAXBElement.getValue(), because it is a JAXBElement that is returned, and a simple (Input) cast simply crashes:

Input input = (Input)unmarshaller.unmarshal( element.getXMLStreamReader() ).getValue(); 

Do you know what leads to such a difference ?

Answer 1

If the root element uniquely corresponds to a Java class then an instance of that class will be returned, and if not a JAXBElement will be returned.

If you want to ensure that you always get an instance of the domain object you can leverage the JAXBInstrospector. Below is an example.

Demo

package forum10243679;  import java.io.StringReader; import javax.xml.bind.*; import javax.xml.transform.stream.StreamSource;  public class Demo {      private static final String XML = "<root/>";      public static void main(String[] args) throws Exception {         JAXBContext jc = JAXBContext.newInstance(Root.class);         Unmarshaller unmarshaller = jc.createUnmarshaller();         JAXBIntrospector jaxbIntrospector = jc.createJAXBIntrospector();          Object object = unmarshaller.unmarshal(new StringReader(XML));         System.out.println(object.getClass());         System.out.println(jaxbIntrospector.getValue(object).getClass());          Object jaxbElement = unmarshaller.unmarshal(new StreamSource(new StringReader(XML)), Root.class);         System.out.println(jaxbElement.getClass());         System.out.println(jaxbIntrospector.getValue(jaxbElement).getClass());     }  } 

Output

class forum10243679.Root class forum10243679.Root class javax.xml.bind.JAXBElement class forum10243679.Root 

Answer 2

It depends on the presence of XmlRootElement annotation on the class of your root element.

If you generate your JAXB classes from an XSD, the following rules are applied:

• if the type of the root element is an anonymous type -> XmlRootElement annotation is added to the generated class
• if the type of the root element is a top level type -> XmlRootElement annotation is omitted from the generated class

For that reason I often choose anonymous types for root elements.

You can customize the class name of this anonymous type with a customization file. E.g. create a bindings.xjc file like this:

<jxb:bindings version="1.0"               xmlns:jxb="http://java.sun.com/xml/ns/jaxb"               xmlns:xs="http://www.w3.org/2001/XMLSchema">     <jxb:bindings schemaLocation="yourXsd.xsd" node="/xs:schema">         <jxb:bindings  node="//xs:element[@name='yourRootElement']">             <jxb:class name="YourRootElementType"/>         </jxb:bindings>      </jxb:bindings> </jxb:bindings>