One of the four steps to setup Java RMI is "Making classes network accessible." Since I'm new to Java RMI, I found this requirement surprising. We have a client and a server. Of the two of them, surely one of the two has a full set of classes. Why require a third server to host the classes?
I suppose they were thinking that somewhere near the RMI server would be a big expensive heavyweight J2EE container, and that thing can serve the classes. But even if I have the J2EE server setup, this is still annoying - I still need to configure the webserver, and then keep it's jars synchronized with the ones my RMI server is using.
Instead, I decided to do the Simplest Thing That Could Possibly Work. I wrote a tiny HTTP Server (168 lines of code) and used it to publish all the classes in my local JVM. Now in my RMI code, I simply need this:
String currentHostname = "jessesmac.publicobject.com";
new RmiClassServer(currentHostname).run();
The RMI server serves classes to anyone who's interested. I don't need to tell it which classpath to use - it uses the exact same classes that the local classloader uses, via Class.getResource.
Sound useful for your RMI application? You'll need RmiClassServer.java and MiniHttpServer.java, both of which are available under your choice of Mozilla 1.1 or LGPL license.
A final word of caution - this server exposes everything on your application's classpath. Unless your classes themselves are public, please don't put this server (or your RMI server!) on your public website.