JSF does not really work like that. The form fields in the view (.jsf or whatever) are mirrored by fields and properties in the bean. They are automatically populated by JSF when the servlet is invoked further up the stack.
This makes the need to read HTTP parameters redundant except when the browser lands on a JSF page from a non-JSF based form. For that something like Spring-MVC can accept the URI being targetted and make a connection to the ManagedBean instance before redirecting the browser to a JSF powered URL.