Existing Plug-and-Play Webapps (Tomcat / JSP)?

I've been working with Tomcat and JSP- I've got a page that takes an input parameter, and based on that parameter, reads an xml file with data on it (it's a smarter version of my code.KevinWorkman.com page). I know that's probably not the most correct way to do things, but at least this way I don't have to change 25 pages every time I make a change on a menu.

I'm venturing into slightly more advanced territory, and I now have login and registration working, as well as the ability to fill out a form that automatically creates a new info.xml file, so you can upload a game without going through the trouble of creating and organizing the same 10 files for each (jnlp file, thumbnail, favicon, background, etc...).

As I'm working on this, I can't help but think that I'm reinventing the wheel. Surely there is an existing login/registration webapp I could just plug-and-play, right? Or a webapp that allows a user to create a blog-like entry, coupled with the ability to upload image files embedded in that entry?

I've done quite a bit of googling, but I keep coming across tutorials on how to create my own webapps- which I certainly can, and have been doing, but I feel like I'm repeating work that has already been done before, by people who actually know what they're doing.

So my question is, is there a collection of existing webapps I can use to just plug-and-play into my system? For example, a webapp that I drop into my webapps folder, and presto (or with minimal setup), I now have registration and login capabilities without writing all the logic to keep track of and update my user's info. Or is all of this so site-specific that it's not really possible to have plug-and-play functionality like that?

I don't know of anything specific, but wanted to suggest searching sourceforge...there might be some projects you could adapt for your own uses (I just did a search for "jsp tomcat login" and saw a few projects, in particular a blog project - might be worth looking at).

Thanks copeg, that's a good idea. I searched through sourceforge, but I didn't find anything as easily plug-and-playable as I was thinking. I suppose that kind of thing is simply too tied into a specific site to be reusable, but I thought that there would have been some kind of modular solution for the generic stuff (user information, uploads, etc).

Anyway, I think I'm going to approach the problem from a different angle. I've been putting off doing any database stuff so as not to bite off more than I can chew, but in the end it's causing me more problems than it's solving. It seems that many of my problems are caused by looking for workarounds instead of just adding a database, when that's probably the most correct solution.

For what its worth, I was browsing the Apache project list today and stumbled upon Apache Click. Might be worth taking a look at. The following has some examples
Apache Click User Guide
There are also other projects like Struts you might want to take a look at.

That looks awesome! You've been a huge help through this whole process, thanks so much. The more I learn about this stuff, the cooler I think it is. I'm still bootstrapping myself through the basics, but I'm definitely going to add that to my bookmarks for when I'm ready to take it to the next level.