Ralph Kar wrote:
> Hi all,
>
> I have a question concerning the new JAXB version 1.0 FCS.
> I want to migrate from the early access version (which was using DTDs)
> to the new schema driven version of JAXB. With the old version it was
> possible to define interfaces (and so inheritance) in a very flexible
> way via interface elements. I have used this technique excessively and
> defined several interfaces.
> With the new version I discovered a problem with the inheritance
> mechanism.
> To my knowledge there is no possibility to define any multiple inheritance
> relationships which was possible with the early access version.
Since XML schema (unlike DTD), provides a way to define inheritance type
hierarchies, the assumption was that the schema would be designed with the
desired inheritance hierarchy. JAXB, then provides a way to map the
inheritance
hierarchy specified in the schema to a Java inheritance hierarchy; support for
this
feature was therefore dropped.
For your particular use case, a <class> customization on an <attributeGroup>
is
be one possibility. But a <class> customization on an <attributeGroup>
is currently not allowed by the specification.
We are investigating this further. Stay tuned.
Thanks for the feedback.
Sekhar Vajjhala - Sun Microsystems.
>
>
> An example:
>
> We have the following elements:
>
> baseA baseB
> ^ ^
> | |
> | |
> elementA --> InterfaceAandB <-- elementB
>
> Furthermore elementA and elementB have some attributes in common.
> This relationship is documented by the fact that both elements
> implement the interface InterfaceAandB.
>
> With JAXB early access this could be expressed:
>
> DTD:
>
> <!ELEMENT baseA EMPTY>
> <!ATTLIST baseA attrC CDATA #IMPLIED
> attrD CDATA #IMPLIED>
>
> <!ELEMENT elementA EMPTY>
> <!ATTLIST elementA attrA CDATA #IMPLIED
> attrB CDATA #IMPLIED
> attrC CDATA #IMPLIED
> attrD CDATA #IMPLIED>
>
> <!ELEMENT baseB EMPTY>
> <!ATTLIST baseB attrE CDATA #IMPLIED
> attrF CDATA #IMPLIED>
>
> <!ELEMENT elementB EMPTY>
> <!ATTLIST elementB attrA CDATA #IMPLIED
> attrB CDATA #IMPLIED
> attrE CDATA #IMPLIED
> attrF CDATA #IMPLIED>
>
> XJS:
>
> <interface name = "BaseAElementA"
> members = "BaseA
> ElementA"
> properties = "attrC
> attrD"/>
>
> <interface name = "BaseBElementB"
> members = "BaseB
> ElementB"
> properties = "attrE
> attrF"/>
>
> <interface name = "ElementAElementB"
> members = "ElementA
> ElementB"
> properties = "attrA
> attrB"/>
>
> With the new version of JAXB you can express the inheritance relationship
> very easily:
>
> <xsd:complexType name="baseA">
> <xsd:attribute name="attrC" type="xsd:string"/>
> <xsd:attribute name="attrD" type="xsd:string"/>
> </xsd:complexType>
>
> <xsd:complexType name="elementA">
> <xsd:complexContent>
> <xsd:extension base="baseA">
> <xsd:attribute name="attrA" type="xsd:string"/>
> <xsd:attribute name="attrB" type="xsd:string"/>
> </xsd:extension>
> </xsd:complexContent>
> </xsd:complexType>
>
> <xsd:complexType name="baseB">
> <xsd:attribute name="attrE" type="xsd:string"/>
> <xsd:attribute name="attrF" type="xsd:string"/>
> </xsd:complexType>
>
> <xsd:complexType name="elementB">
> <xsd:complexContent>
> <xsd:extension base="baseB">
> <xsd:attribute name="attrA" type="xsd:string"/>
> <xsd:attribute name="attrB" type="xsd:string"/>
> </xsd:extension>
> </xsd:complexContent>
> </xsd:complexType>
>
> The Interface between elementA and elementB is a bit harder:
>
> <xsd:attributeGroup name="ElementAElementB">
> <xsd:annotation>
> <xsd:appinfo>
> <jxb:class name="ElementAElementB"/>
> </xsd:appinfo>
> </xsd:annotation>
> <xsd:attribute name="attrA"/>
> <xsd:attribute name="attrB"/>
> </xsd:attributeGroup>
>
> <xsd:complexType name="elementA">
> <xsd:complexContent>
> <xsd:extension base="baseA">
> <xsd:attributeGroup ref="ElementAElementB"/>
> </xsd:extension>
> </xsd:complexContent>
> </xsd:complexType>
>
> With the jxb:class tag you can ask JAXB to generate the interface.
> This is where the problem occurs. There seems to be no way to
> convince JAXB to make ElementA implement the interface ElementAElementB.
> Since every element will be represented as an interface there should be no
> reason to deny inheritance from more than one interface.
> Another possible solution would be to allow more than one extension
> element within a complexContent element. Since JAXB only creates code
> which inherits interfaces that should not be a problem either.
> As long as JAXB does not provide possibilities to inherit from more than
> one interface it is not as powerful as the early access version has been.
> Any comments or advice to my problem will be greatly appreciated. If I
> have missed something helpful in the JAXB spec or user guide please let me
> know.
>
> Greetings,
> Ralph
>
> -----------------------------------------------------
> Ralph Kar |
> Software Developer | mailto:r.kar_at_rtsgroup.net
> RTS Realtime Systems AG | http://www.rtsgroup.net
> -----------------------------------------------------