Parameters may not be set, and are not interchangeable with attributes.
Parameters come from form elements, or from being appended to the url query (the portion after the ? you'll see in the address bar if you use method=get)
Part 2 sort of contradicts what I just said about not being able to set them, what I mean is that there is no setParameter defined in HttpServletRequest.
You can add a hidden field to the form and add the parameter that way, or use set/getAttribute