docs: @Override
      public void contextInitialized(ServletContextEvent sce) {
          final ServletContext servletContext = sce.getServletContext();
          if (servletContext.getAttribute(PortletApplicationContextUtils2.ROOT_PORTLET_APPLICATION_CONTEXT_LOADER_ATTRIBUTE) != null) {
              throw new IllegalStateException(
                      "Cannot initialize root portlet ContextLoader context because there is already a root PortletContextLoader present - " +
                      "check whether you have multiple PortletContextLoaderListener definitions in your web.xml!");
          }
          
          //Register the portlet context loader with the servlet context
          contextLoader = new PortletContextLoader(servletContext);
          servletContext.setAttribute(PortletApplicationContextUtils2.ROOT_PORTLET_APPLICATION_CONTEXT_LOADER_ATTRIBUTE, contextLoader);
      }