If you’re using JSPs, then just use JSPs and don’t worry about it.
If you’re using Vaadin, then Vaadin is handling the form and will deal w/ the issues.
Vaadin is not a server side framework on it’s own - it uses a lot (in fact almost all) AJAX for communicating between the browser and the server, and trying to mix things in this way is doomed to failure.
Thanks for your answer Dave. I need to communicate an app not coded in vaadin (JAVA+FLEX) with a new vaadin app sending some not invisible parameters (from the Flex app I need to open a browser window containing the vaadin app). So I’m trying with a form with POST method. If someone have a better idea I’ll be grateful.