2.2.16.2
Another Content Tree as Element
It's also possible to insert an arbitrary content tree as an element.
We'll assume that we have several document definitions, like this:
<xsd:complexType name="HearsayType">
<xsd:sequence>
<xsd:element name="text" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="GrapevineType">
<xsd:sequence>
<xsd:element name="text" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="RumourType">
<xsd:sequence>
<xsd:element name="text" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
We want any of these nice documents to be envelopped by a container
document:
<xsd:complexType name="CommType">
<xsd:sequence>
<xsd:element name="source" type="xsd:string"/>
<xsd:element name="comm" type="xsd:anyType"/>
</xsd:sequence>
</xsd:complexType>
There is no surprise in the classes generated by the JAXB compiler.
(The comm sub-element of CommType has the
type java.lang.Object.) So we can write some code to
marshal such an XML communication.
ObjectFactory of = new ObjectFactory();
// Create the container object.
CommType comm = of.createCommType();
comm.setSource( "Ms Jones" );
// Let's have some hearsay.
HearsayType hearsay = of.createHearsayType();
hearsay.setText( "Mr. Harper does naughty things." );
comm.setComm( hearsay );
// Prepare a JAXBElement, ready for marshalling.
QName qn = new QName( "comm" );
JAXBElement<CommType> je =
new JAXBElement<CommType>( qn, CommType.class, comm );
The JAXBElement is now ready to be passed to a
Marshaller. The resulting XML text looks like this:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<comm>
<source>Ms Jones</source>
<comm xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:type="HearsayType">
<text>Mr. Harper does naughty things.</text>
</comm>
</comm>
It should be satsifying to note that JAXB has annotated the
comm element with xsi:type="HearsayType"
which is going to help a lot during the inverse process. In fact,
all you have to do to get this document unmarshalled into a
content tree and to access the nested contents is this:
File f = new File( ... );
JAXBElement<CommType> je = (JAXBElement<CommType>)u.unmarshal( f );
CommType comm = (CommType)je.getValue();
if( comm.getComm() instanceof HearsayType ){
HearsayType hearsay = (HearsayType)comm.getComm();
} else {
// ...(investigate other possibilities)...
}