You can't have two parameters in a request with the same name.
This is possible but not with the javax.faces API. You would have to fall back to the servlet API.
Note the differences:
I think something like this should work:
ServletRequest request = (ServletRequest)FacesContext.getCurrentInstance().getExternalContext().getRequest(); // the map contains keys as String and values as String  Map params = request.getParameterMap();
I have just discovered that:
1. redirect filter must be enabled to append parameters to URL
2. javax.faces.STATE_SAVING_METHOD must be set to client - according to BLOG example (when I tried to set to server, then it stops work)
It is required to save state on client?
sorry previous comment belongs to other thread
i use FacesContext.getCurrentInstance().getExternalContext().getRequestParameterValuesMap().get("paramName")