issue with setAttribute into a servlet

I try to pass attributes to a request into a servlet, but somehow it does not seem to work:

try{
        request.setAttribute("str","test");
        request.setAttribute("compt",compt);
        request.setAttribute("raton",raton); //I tried with different types

// request.getParameterMap().size() always evaluate to 0 instead of "the number of arguments"

Map<String, String[]> parameters = request.getParameterMap(); 
        for(String parameter : parameters.keySet()) { //is never looped

                String[] values = parameters.get(parameter);

                for(String v : values) out.println(v);

        }



        request.getRequestDispatcher("/index.jsp").forward(request, response);
        }
        catch(Exception ex){
            ex.printStackTrace();
        }

And of course consequently, I get no attribute when parsing the request into the JSP. Did I miss something??

Thx in advance