code: public void processEvent(SystemEvent event) throws AbortProcessingException {
  		FacesContext context = FacesContext.getCurrentInstance();
  		UIViewRoot root = context.getViewRoot();
  
  		// render the resources only if there is at least one bsf component
  		if (ensureExistBootsfacesComponent(root, context)) {
  			addCSS(root, context);
  			addJavascript(root, context);
  			addMetaTags(root, context);
  		}
  	}
docs: Trigger adding the resources if and only if the event has been fired by
  UIViewRoot.