Hey rejeep,
I think the reason you probably haven't found anything specific about Applets and Rails is that they function a bit at different levels and aren't really dependent on one another. It looks like Rob was trying to clarify a few things, so I'll take it another step just to be sure we are all on the same page.
The job of Rails is to generate and serve up HTML/XML/Javascript/images via a web server to the user's web browser for rendering. Part of that HTML will be an APPLET (or possibly OBJECT) tag, which instructs the browser to load the applet. Usually, this instructs the browser to invoke the Java Plug-in and lets it handle loading the applet. Once loaded and running, however, even though the applet is displayed on the current web page in the browser (or maybe in another window even), it really isn't terribly aware of the web page it is sitting in. For the most part, applets don't care about the browser or the page they are "part of". So if an applet needs more information, or needs to ask for data, it usually will just send an HTTP request to the server it came from. It would then parse the data and update itself.
I am assuming what you probably need is for something to be clicked or entered into the applet, and that data be used to update the web page that Rails is serving to the browser. With an applet, you pretty much have 2 options:
- Use the web server application to share state information
- Use the Java-to-Javascript communication using JSObject as indicated at http://java.sun.com/products/plugin/1.3/docs/jsobject.html
Honestly, option number 2 comes with so many caveats, that I would never use it unless you had complete control over browser and Java versions on all potential users' systems. Even then, I'd be concerned of an update to something breaking it.
Basically, option number 1 leaves you with the Applet and the Javascript/HTML polling the web server (Rails) periodically to see if there are any updates or requests that they need to respond to for data exchange. If the applet is updated by the user, it sends a message to the web server via a URL request/post and the next query (probably via an AJAX-like call) by the web page will see the new data and the web page will be updated with it.
I hope that helps.