Forms and anchor tags don't have anything to do with each other. Putting an anchor in a form has no special semantic meaning.
I'm still unsure what your question is at this point. The easiest way to invoke Java on the server as a result of a client side action, without the need to submit the whole page, is via an Ajax call to a servlet. What's the issue at this point?
In any case, if you need to use Ajax without jQuery or other library, this article is a good place to start.