Does it have to be Java-based? If not, and if you're not looking to take advantage of specific features in the editor application, you might want to take a look at the Mozilla platform. No practical dev experience with it, but from the look of the documentation it appears to offer a relatively simple way to create a cross-platform rich client. I believe there is also a Mozilla dev group looking at ways to hook Java into Mozilla, which would let you leverage work you may have already done in Java.

I use a couple of Mozilla-based apps (aside from Firefox), and it's not bad. It has its quirks, but I think there is tremendous potential in the platform.