Hi,
In order to add functionality to a class generated by JAXB, one has two
options: inheritance or delegation. Inheritance is dodgy because of
brittleness, the equals() contract, and appropriateness of this
mechanism. As was pointed out in an earlier post, is XMLCustomer really
a valid new type of Customer?
Delegation, then, involves creating a class with the binding object as a
member variable. Take BarDelegator with a member variable of Bar. It
needs to implement the Bar interface as well, and delegates all Bar
methods to the member variable. Additional methods with extra
functionality can be added normally. Well and good.
However, BarDelegator, in order to participate in the JAXB marshalling
process, needs to do more. If you have interface Foo containing method
'getBar();' and 'setBar( Bar bar );', you will run into trouble
marshalling a Foo which has had 'foo.setBar( barDelegator );' called on
it. BarDelegator needs to implement 3 extra interfaces from jaxb-ri.jar,
namely:
com.sun.xml.bind.unmarshaller.UnmarshallableObject
com.sun.xml.bind.serializer.XMLSerializable
com.sun.xml.bind.validator.ValidatableObject
If the methods these create in BarDelegator all delegate to the Bar
member variable as before, all is well.
No doubt this is old hat to experienced JAXB developers, but my question
is: Is this a valid use of public API? The use of Suns interfaces seems
to suggest not. If not, how 'published' are Suns interfaces? Are there
any other ways to extend functionality of a jaxb class?
TIA,
Craig
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