code: public static ActivityContext getActivityContext(ServletContext servletContext) {
          ActivityContext activityContext = getActivityContext(servletContext, ROOT_WEB_SERVICE_ATTRIBUTE);
          if (activityContext == null) {
              throw new IllegalStateException("No Root AspectranWebService found; " +
                      "No AspectranServiceListener registered?");
          }
          return activityContext;
      }
docs: Find the root ActivityContext for this web aspectran service.
  
  @param servletContext ServletContext to find the web aspectran service for
  @return the ActivityContext for this web aspectran service