Have you tried executing your code in the debugger of a good IDE? That's how
I find problems in my servlets. I use Eclipse but there are other good IDEs
as well; I've heard good things about Net Beans for example, although I've
never used it.

That would help you figure out if your LinkedList is empty or not; if it is
empty, you could figure out why.

The while(rs.next()) in your code fragment strongly suggests that you are
looping through an SQL result set and using values obtained from that result
set to populate your DataPair object. Are you aware that if the result set
is empty, the while() loop will not execute even once. That could explain
why your DataPair object is empty - if it is - and could also explain why
your graph doesn't display any points. I would suggest looking at your SQL
to see if it might possibly have a mistake in it or be pointing at an empty
table instead of the one that has the expected data.

Rhino