What I'm looking for is a scripting engine for Java that would allow users to write simple scripts to control the behavior and events for a game. Something that:
is simple - something easy to pick up, especially for people with some basic programming/scripting experience
provides lots of control - I can easily start/stop/pause scripts and control how much execution time each gets, perhaps how much memory space they can use
is separated from the Java environment itself - No access from scripts to any Java objects or classes, only to those functions I explicitly provide
I've considered the Rhino JavaScript engine, and it would suit my purposes, but from what I've read (example), it's designed to integrate with Java so much that sandboxing it securely would be tricky. I'd rather start with an engine that gives scripts no access to anything by default, than have a fully open one that I have to close up. The scripts might not always be trusted, so the environment should not be easy to break out of.
I'd also consider developing my own language with something like ANTLR, but it's probably more effort than I want to put in.
Any suggestions?