How to load, compile, and call a JRuby file, from Java?

Question

The best doc I found was this, but it's a bit outdated -- deprecated or missing methods. I'd like to, from Java code:

1. Load a .rb file from the filesystem.
2. Make sure it is compiled to the fastest form possible, since this exists in a long-running server.
3. Call a function or class in that file, passing in values constructed on the Java side.
4. (If possible) Be able to repeat steps 1-3, if the .rb file changes, and pickup the new Ruby code.