Create an XML import service

I want a service that I can call (from a plugin in my case, but it could be from anywhere) that will create a new object from an XML file. Ideally I would only need to provide the file and the user, and everything that needs to be discovered about the object and where it goes could be read out of the XML.

The specific use case I have in mind is creating an image assessor (a Freesurfer assessor, for example) at the end of a container execution. When a container finishes, an event is fired that will kick off "container finalization" tasks; one of those may be finding XML files that have been generated and creating assessors from them. It would be very nice if all the container service had to do is find the file and pass it along to some service within XNAT proper that could do the rest of the job.

Similar in spirit to XNAT-4548. Here, I want an XML file -> Assessor/Whatever service; in XNAT-4548 I wanted a directory -> Resource service.