JRuby interops fine with Java. Any specific thing you might be curious about?
One example is Rack applications are hosted by Java web containers Just Fine via a server -> Rack mapping. We use this in production for both a Sinatra app and a Rails app.
Interesting! Does that (partially) obsolete this answer [0]? Do Ruby programs see Java objects as a separate kind of Object, or is it seamless? Is there a translation layer anywhere? Does JRuby-Rack have to use wrappers for Java functions?
One example is Rack applications are hosted by Java web containers Just Fine via a server -> Rack mapping. We use this in production for both a Sinatra app and a Rails app.