The fact that JAXBSource derives from SAXSource is an implementation
detail. Thus in general applications are strongly discouraged from
accessing methods defined on SAXSource. In particular,
the setXMLReader and setInputSource methods shall never be called.
The XMLReader object obtained by the getXMLReader method shall
be used only for parsing the InputSource object returned by
the getInputSource method.

Similarly the InputSource object obtained by the getInputSource
method shall be used only for being parsed by the XMLReader object
returned by the getXMLReader.