cross domain DOM access and manipulation in Java?

In my Java app, how can I incorporate the browser (which loads and renders URLs) in Swing and access it's DOM and manipulate HTML ?

How can you embed such browser in a Rich Internet Application and access it's DOM ? More specifically, Vaadin ? Is there a HTTP proxy class that can load an external URL, and render it to the user ? This was what I was doing on LAMP stack....but I want to switch to Vaadin or some Java web framework where I can just use Java to do everything from server-side to client-side logic design, so I can focus more on application logic. (aka looking for developer friendly frameworks like Vaadin).

Thank you and have a great weekend !

NetBeans have been making strides in this direction. See their wiki, but I don't think they can get hold of the DOM.