A Java-based intranet?

OK, so we showed pMachine and TWiki to our HR and marketing folks. In general, they seemed to like what they saw. There was, however, some real hesitation about TWiki's central idea of letting any user modify any page (just what we'd need: Some joker adding "unlimited free beer" to the benefits page) , but fortunately, you can lock down parts of a TWiki site to keep that from happening.

But not so fast there. ...

One of them asked "How much does the software cost?" You, of course, know the answer: The initial cost (which in this case would be a maximum of $125) is only a fraction of the true cost of any software project.

Later in the day, I went over to see our senior programmer, who isn't involved in this project, about something unrelated. We started talking about this intranet thing and he raised some good points about architecture and back-end support. A couple of years ago, Network World decided to make Java its primary application-development language. Our programmers all knew it and we liked the scalability of server-side Java.

So along comes Mr. Web Editor with his PHP and Perl apps for the corporate intranet. In a word: Feh! Now, there's the "best tool for the job" argument - both the PHP and Perl apps already do much of what we want and would be easy to set up and easy for end users to use. But long term, is this the best decision? Already, if we use pMachine, I know we'd have to hack one script to give the marketing department the ability to attach files to pages in the system. What happens in the future with such requests, after I've gone on to other things and this intranet has taken off? It'll fall to IS, right? I have no doubt our programmers, quick learners all, could easily figure out the basics of PHP and make further mods. But if we started with a Java app to begin with, they wouldn't have to spend any time learning a new language - they'd just do it.

So, anybody know of any decent open-source or low-cost Java community applications out there? To recap: We want a system that can be administered and updated through a Web interface, that lets multiple people contribute content and allows for different templates for each department and that has some sort of search, forum and calendar functions (I know there are Java-based wikis out there; does anybody know how they compare to TWiki in terms of such things as access control and templating?). Thanks in advance for any suggestions!