docs: public void startProcessInstanceByIdForm() {
      if (FacesContext.getCurrentInstance().isPostback()) {
        // if this is an AJAX request ignore it, since we will receive multiple calls to this bean if it is added
        // as preRenderView event
        // see http://stackoverflow.com/questions/2830834/jsf-fevent-prerenderview-is-triggered-by-fajax-calls-and-partial-renders-some
        return;
      }
  
      Map<String, String> requestParameterMap = FacesContext.getCurrentInstance().getExternalContext().getRequestParameterMap();
      String processDefinitionId = requestParameterMap.get("processDefinitionId");
      String callbackUrl = requestParameterMap.get("callbackUrl");
      this.url = callbackUrl;
      this.processDefinitionId = processDefinitionId;
      beginConversation();
    }