Built in JAXB XML Providers

As required by the specification, RESTEasy JAX-RS includes support for (un)marshalling JAXB annotated classes. RESTEasy provides multiple JAXB Providers to address some subtle differences between classes generated by XJC and classes which are simply annotated with @XmlRootElement, or working with JAXBElement classes directly.

For the most part, developers using the JAX-RS API, the selection of which provider is invoked will be completely transparent. For developers wishing to access the providers directly (which most folks won't need to do), this document describes which provider is best suited for different configurations.

A JAXB Provider is selected by RESTEasy when a parameter or return type is an object that is annotated with JAXB annotations (such as @XmlRootEntity or @XmlType) or if the type is a JAXBElement. Additionally, the resource class or resource method will be annotated with either a @ConsumeMime or @ProduceMime annotation and contain one or more of the following values:

• text/+xml

• application/+xml

• application/fastinfoset

• application/json

RESTEasy will select a different provider based on the return type or parameter type used in the resource. This section decribes how the selection process works.

@XmlRootEntity

When a class is annotated with a @XmlRootElement annotation, RESTEasy will select the JAXBXmlRootElementProvider. This provider handles basic marhaling and and unmarshalling of custom JAXB entities.

@XmlType

Classes which have been generated by XJC will most likely not contain an @XmlRootEntity annotation. In order for these classes to marshalled, they must be wrapped within a JAXBElement instance. This is typically accomplished by invoking a method on the class which serves as the XmlRegistry and is named ObjectFactory.

The JAXBXmlTypeProvider provider is selected when the class is annotated with an XmlType annotation and not an XmlRootElement annotation.

This provider simplifies this task by attempting to locate the XmlRegistry for the target class. By default, a JAXB implementation will create a class called ObjectFactory and is located in the same package as the target class. When this class is located, it will contain a "create" method that takes the object instance as a parameter. For example, of the target type is called "Contact", then the ObjectFactory class will have a method:

public JAXBElement createContact(Contact value) {..

JAXBElement<?>

If your resource works with the JAXBElement class directly, the RESTEasy runtime will select the JAXBElementProvider. This provider examines the ParameterizedType value of the JAXBElement in order to select the appropriate JAXBContext.