I don't really understand what that is supposed to do.
You have an XSL transformation which is generating HTML. The HTML which it generates contains an <input> element. And
you want to get data from that element??? That doesn't make any sense at all. The element doesn't contain any
data. When the HTML is rendered by the browser and the user looks at the form, the user might key something into
the element at that point, but that happens long after this transformation has finished.
And you want to "call a servlet"? And "get a value"? Does that mean you want to send a request to a server, where
that servlet will be invoked and return a response, and then extract some data from that response? It does help if
you call things by their real names. Also, as before, that form won't send a request until it is in front of a user.
So, I don't know what you are really trying to do there, but whatever it is, that isn't the right way to do it.
You should
try to reframe your requirements in terms of XSLT generating HTML, the browser rendering it, the user clicking on
something which sends a request, and so on.