You can program the JSP to execute some Javascript while it is loading on the client, and could have that Javascript call the server for some data.
These lines execute some action on the server.
The 'url' parameter is the URL to call
parseResult is a function that parses the returned data into the control (use innerHTML property).
This quite possibly will work
only in IE 5.5 and up.
What you can NOT do is have the server execute a script on the client (the onload function happens only after the response has started sending to the client at which point you can't do much about it anymore.