What functionality?  Depending on the level, HTML/JS
might be quite enough to achieve it.

Try this for a thought.  After 'functionalising' the data,
the user can post it to a second page that is either..
- a plain HTML table, with a link below to the same as CSV, or..
- the CSV file itself.  Most browsers will offer to save a CSV file,
  though your poor IE users might need instructions, as IE would
  likely open the CSV in whatever program is registered to handle
  a CSV file (often Excel).

That could be an HTML table. You might check the CSS newsgroups for
discussions of how to have non-scrolling headers and footers, a cause
of much teeth gnashing.

You could do the display with a JTable Applet with a local cache of
rows backed by the server.  If the table is large, this is what you
will need.

To export the CSV you could have a button that downloads a virtual
file you compose.  See http://mindprod.com/jgloss/csv.html

You could also have the signed Applet or JAWS Applet/application
create the CSV file.  That would be faster since the Applet would
already have most of the data and the data could be sent to the Applet
in compressed from rather than as a raw CSV.

If that makes your head ache, I am open for contract work.