Saxon

I'm afraid I don't know enough about MapForce to help with this one. I do know that Altova's and Saxon's conventions for calling extension functions are quite different, but there might be some common subset you can use.

Saxon has "reflexive extension functions" which are quite similar (all the Java products have similar mechanisms, but the rules differ in detail). The Saxon mechanism is documented here: http://www.saxonica.com/documentation/index.html#!extensibility/functions

For calling static methods, which is the simplest case, you use a namespace like java:java.util.Date to identify the Java class, and the local name to identify the method within the class, and there is a defined set of mappings from XPath types to Java types for converting the parameters and the result. It's likely that in simple cases (strings, integers etc) these will be the same as the mappings used by Altova. If necessary you can use the "use-when" attribute so your stylesheet has different code for the Saxon and Altova cases.

Your example has a "path" parameter as part of the namespace; that isn't something Saxon supports. In Saxon, the class is always loaded from the classpath.