You don't. You assemble a form or hyperlink to the action and invoke it via an HTTP POST or GET operation. PLEASE do not try to invoke a method in an action class directly from a JSP! This ties your view directly to your controller, and suddenly you might as well not be using MVC at all!
"Write beautiful code; then profile that beautiful code and make little bits of it uglier but faster." --The JavaPerformanceTuning.com team, Newsletter 039.