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.
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
-----------------------------------------------------