This question is unanswerably broad. What kind of games are you talking about? What do you mean by a server for these games? Are you writing your own MMPORPG that will need it's own server application or hosting a couple of jsp based card games that can run through the normal java server applications?
Try splitting this up into a few more detailed questions, or providing a whole lot more detail on thisone.
So you are approximately talking about something jsp based? In that case the features are pretty much whatever you want them to be- anything you have seen another website do you can do with JSP. The only things it is not so good for are ones needing constant data-pushing because the way the web works is that I ask for a web page and the server sends me one. The server doesn't constantly send pages.
Basically you need to think about what you want to do and design it accordingly. Download Tomcat and experiment with that. You will probably find most of your questions will already have been answered on the JSP forum here, so use the search facility a lot. Most of the issues you encounter will be more on the web side, rather than the gaming side, I would expect.