Instead of the JSR requirements :
Return an immutable Map whose keys are the set of request parameters names included in the current request, and whose values (of type String) are the first (or only) value for each parameter name returned by the underlying request. The returned Map must implement the entire contract for an unmodifiable map as described in the JavaDocs for java.util.Map
This Map must be composed from the set of parameters available via the javax.portlet.PortletRequest methods getParameter() and getParameterNames() plus any additional parameter names encoded in the (query string) of the viewId. This later situation primarily occurs when using a default viewId provided by the portlet.
In addition, during a portlet's RENDER_PHASE, if not otherwise already in the Map, the bridge must include those parameters managed in the corresponding bridge request scope. This always includes the ResponseStateManger.VIEW_STATE_PARAM parameter. The preservation/inclusion of the rest of the action parameters depends on the javax.portlet.faces.[portlet name].preserveActionParams portlet context attribute. If this context attribute exists and has a value of Boolean.TRUE, the additional action parameters are preserved/included, otherwise they aren't.
RequestParametersMap contain an only action parameters.