I cannot find an example or indication on how to call XML Calabash (an Xproc implementation) to be run from Java. The requirements are simple:
List item Be able to work concurrently since we want it to be a process running in a Jetty Server
You should have a look at Servlex and in particular here https://github.com/fgeorges/servlex/tree/master/servlex/src/java/org/expath/servlex/processors
Hope this helps