Namespace-aware XPath expression

[Jesus M. Salvo Jr.]

How do you get a node via XPath that is namespace-aware?

I realise it has to do with the PrefixResolver that you pass in as an argument 
to either the XPath constructor or to the XPath.execute(), but I am not sure 
how to go about it.

e.g.:
1) Do you need to pass the same resolver in both the constructor and the 
execute method?
2) How do I specify my expressions?

Take for example this fragment of XML

<mm7:SubmitReq 
xmlns:mm7="http://www.3gpp.org/ftp/Specs/archive/23_series/23.140/schema/REL-5-MM7-1-2";>
<mm7:MM7Version>5.5.0</mm7:MM7Version>
<mm7:SenderIdentification>
        <mm7:VASPID>MIG</mm7:VASPID>
        <mm7:VASID>Mig-test4</mm7:VASID>
        <mm7:SenderAddress>
                <mm7:Number>+6140955555</mm7:Number>
        </mm7:SenderAddress>
</mm7:SenderIdentification>

... The above SubmitReq element is not the root element, but is obtained 
via Apache-SOAP:

   Node      submitReqNode = (Node) envelope.getBody().getBodyEntries().get( 0 
);

Now once I got the SubmitReq node above, here's what I do:

   PrefixResolverDefault resolver = new PrefixResolverDefault( submitReqNode );
   XPath xpath = new XPath( "//SenderIdentification/SenderAddress/Number", 
this.locator, resolver, XPath.SELECT );
   XObject xobject = xpath.execute( context, submitReqNode, resolver );
   String senderString = (String) xobject.castToType( XObject.CLASS_STRING, 
context );

The above code will not retrieve the the number +6140955555.
... but it will if I remove the mm7 prefixes.

So what do I need to do?
I would have assumed that PrefixResolverDefault would have been namespace-aware.