Excellent overview of Swing-based Java HTML browsers:

I hope this article has shown that there is quite a variety of HTML rendering options beyond what's built into Swing. If you can use a commercial license, then there are several excellent options available. I would choose a package based on your own price point and customization needs. On the open source side, JRex has the potential to be a great native wrapper solution, and I would say that MultiValent is the best 100-percent-Java project. My biggest disappointment is the lack of advanced CSS support. Some of the commercial browsers do pretty well, but none has the full CSS2 compliance of Mozilla.

Good stuff. The bad part about Java from my pov is how difficult it is to get something up and running quickly -- case in point here is that the open source efforts don't quite measure up -- but there's enough demand for commercial developers (who likely started development for an internal project, I'm guessing) to sell something that's pretty high-quality. Java as a platform is very headless/server-centric, obviously, and it'll be a while before Swing challenges Windows.Forms (or your native widget toolset of choice), if at all.