It's been an awful long time since I thought about Java applets.
A while ago I updated a Java jigsaw application, Sphaero 2, and it was just a regular desktop application. Recently I got asked if it was possible to use it in a web page - as an applet.
This turned out to be incredibly easy. In parallel with the main application (which is a JFrame), implement the same code as part of a JApplet. Took me a few minutes to do (and a bit longer to clean it up and refactor it), so if you go to the Sphaero 2 page there are now a number of sample images that will launch a Java applet if you've got Java support in your browser.
Encouraged by this, I added applet support to JKstat. The idea is to set up a JKstat server, and if you point a web browser directly at the server then you get a page containing the JKstat applet, which can then connect back to the server it was downloaded from (the applet security model says that you can connect back to where you came from, so that's OK) to gather statistics.
This proved to be a little harder. It looks like this only works (in the case of an unsigned applet) for the REST variant of the client-server protocol. If I try it with XML-RPC then it looks like it wants to get DTDs for validation, and gets security exceptions trying to get them. So the standalone JKstat server doesn't work as is.
But that's not too bad, because I've got several options for serving the data using the REST protocol. From my sample play server, to node-kstat, or I've been testing a RESTful server based on Jersey.
It's been a useful learning exercise, and I actually find the results to be quite useful. Maybe applets will become fashionable again?