jnlp not honoring custom xml parser property?

[Dan Rollo]

First, apologies if I'm in the totally wrong place to ask this. Please 
steer me as needed.

My java webstart app uses <property> tags in the jnlp to override the 
default xml parsers, like so:
...
         <property name="javax.xml.parsers.DocumentBuilderFactory"
             value="org.apache.xerces.jaxp.DocumentBuilderFactoryImpl"/>
         <property name="javax.xml.parsers.SAXParserFactory"
             value="org.apache.xerces.jaxp.SAXParserFactoryImpl"/>

         <jar href="lib/sax.jar"/>
         <jar href="lib/dom.jar"/>
         <jar href="lib/jaxp-api.jar"/>
         <jar href="lib/xercesImpl.jar"/> <!-- NOTE: This jar contains: 
org.apache.xerces.jaxp.DocumentBuilderFactoryImpl.class -->
         <jar href="lib/xalan.jar"/>
...

This works fine on ubuntu and many other places, but on my niffty new 
Raspberry Pi, I'm getting an error as if the Service Provider contract 
is not being honoured, and/or as if the class in not in a jar on the 
classpath.
Here's the error trace snippets:

Exception in thread "AWT-EventQueue-1" 
javax.xml.parsers.FactoryConfigurationError: Provider 
org.apache.xerces.jaxp.DocumentBuilderFactoryImpl not found
	at 
javax.xml.parsers.DocumentBuilderFactory.newInstance(DocumentBuilderFactory.java:127)
	at 
com.bhaweb.studioE.model.DTDResolverStudioE.createDocumentBuilderStudioE(DTDResolverStudioE.java:69)
...
Caused by: java.lang.ClassNotFoundException: 
org/apache/xerces/jaxp/DocumentBuilderFactoryImpl
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at javax.xml.parsers.FactoryFinder.getProviderClass(FactoryFinder.java:123)
	at javax.xml.parsers.FactoryFinder.newInstance(FactoryFinder.java:170)
	at javax.xml.parsers.FactoryFinder.newInstance(FactoryFinder.java:147)
	at javax.xml.parsers.FactoryFinder.find(FactoryFinder.java:211)
	at 
javax.xml.parsers.DocumentBuilderFactory.newInstance(DocumentBuilderFactory.java:121)
	... 50 more


I'm running OpenJDK on my RaspberryPI running Raspbian:

$ uname -a
Linux raspberrypi 3.2.27+ #250 PREEMPT Thu Oct 18 19:03:02 BST 2012 
armv6l GNU/Linux

$ java -version
java version "1.7.0_07"
OpenJDK Runtime Environment (IcedTea7 2.3.2) (7u7-2.3.2a-1+rpi1)
OpenJDK Zero VM (build 22.0-b10, mixed mode)

Any other info I can provide?

Thanks!
Dan Rollo