HashMap vs. Map

[Mike Haller]

Hi all,
using Axis 1.2
I'm trying to implement my own service:
public interface MyService {
    public org.w3c.dom.Document listObjects(java.util.Map parameters);
}
Sadly, the generated code (java2wsdl and then wsdl2java) is generating 
this interface:

public interface MyService extends java.rmi.Remote {
    public org.w3c.dom.Document listObjects(java.util.HashMap in0) 
throws java.rmi.RemoteException;
}

Note the difference: Map and HashMap in the method signatures.
Why is it using HashMap instead of Map?
To solve this, i tried to implement my own GeneratorFactory, but failed 
to find the location where the mapping is resolved. I also found out 
that there are <typeMapping> elements - but where do I have to add them, 
since the WSDL file is regenerated on each build.

So, I hope someone can tell me where I can tell Axis' wsdl2java to use 
Map instead of HashMap.

Thanks,
regards
Mike