Since you said you didn't know where to begin I'll just start throwing around a few things to get you thinking. Hopefully they make sense; if not -> that's why we have these forums.
Web applications in Java use the
Servlet and
JSP APIs. Servlets are for writing server-side code that reacts to HTTP requests, and JSPs are a templating technology somewhat akin to PHP. They're generally used together: servlets accept the requests, parse the parameters, and execute the logic, while JSPs then generate the HTML output.
You'd need a server that can handle Servlets/JSP, a so-called servlet container. A very capable one is
Tomcat by the good folks at Apache. It also doubles as a regular web server, so you don't need to set up an additional Apache httpd to go with it (like you'd need for PHP).
As for charts that change over time and can refresh themselves, there's a very capable library called
JFreeChart that creates images out of data. It integrates nicely with JSP pages via the
cewolf library. You can find links to both -plus introductory material- in the
OtherOpenSourceProjectsFaq. If you embed such a chart in a web page that refreshes itself automatically every N seconds you would have what you're asking (I'm assuming that the page refresh isn't itself the problem, but rather the manually required invocation of same). But you probably need to become proficient at servlets/JSP before tackling the charts.
Lots of information to ponder and be confused about. But not to despair - we have forums for all these topics right here at JavaRanch, so don't hesitate to ask.
[ February 04, 2008: Message edited by: Ulf Dittmer ]