mapping form fields to database and handling multiple users

I've written a Web-based application that allows users to log in and edit 
profile data associated with their username.  Right now the application 
consists of perl code written from scratch, and for each username, the 
"database" storing information for that username is just a flat text file.

The perl code I've written actually does an OK job -- handling logins for 
multiple users just involves checking a username and password against a 
text file, and then reading another text file that stores the user's 
settings, and filling in the correct values in form fields.  Sometimes it's 
an advantage that I've written everything from the ground up -- for 
example, I wanted to have a field in the user's settings file that 
indicated whether the user had changed a particular setting in the last 24 
hours.  I just added new "Fieldname_HasChanged" field, and altered the 
update code so that the new value would be checked against the old value, 
and "Fieldname_HasChanged" would be set to 1 if they were different.  If I 
had been using an out-of-the-box solution, I doubt if that kind of 
low-level tinkering would have been possible.

On the other hand, since I'm about to rewrite the application using a more 
scalable language and a better database system anyway, are there pre-built 
solutions already out there for handling either or (ideally) both of the 
following situations:

- The site stores accounts for multiple users.  Users log in through a form 
on the main page; the system hides the details of how user login states are 
maintained (through cookies, or cryptic URL strings, or whatever).  While 
logged in, users can view multiple pages whose content depends on the 
user's account details.

- The server stores data associated with each user.  When a user logs in to 
the site, they see a page containing form fields with values filled in 
corresponding to the user's data.  They can edit and update their data by 
changing the values in these form fields and clicking an Update button.

Both of these are, admittedly, not very hard to code by hand, but a 
pre-built solution would decrease the chances of some tiny logic error 
creeping in and trashing large amounts of user data.

Ideally I'm looking for a way to do it in server-side Java, since Java is 
the language that the application will probably be re-written in.  (I have 
to stop using perl since I've found that I can write code much, much faster 
with statement completion and drop-down fill-in-the-blank capability in my 
code editor, which means I have to use some language supported by Visual 
Studio.  Of course this means I have to put up with a lot of ribbing from 
friends who eat assembly code for breakfast.)

	-Bennett

bennett(at)peacefire.org     http://www.peacefire.org
(425) 649 9024

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