code: static List<ServletContextListener> getDefaultOtherListeners() {
      try{
        Class<ServletContextListener> introspectorCleanupListenerClass = 
            (Class<ServletContextListener>) Class.forName("org.springframework.web.util.IntrospectorCleanupListener");
        return singletonList(introspectorCleanupListenerClass.newInstance());
      }
      catch (ClassNotFoundException e) {
        // Ignore silently - Spring not present on classpath
      }
      catch(Exception e){
        e.printStackTrace(System.err);
      }
      return emptyList();
    }
docs: Get the default set of other {@link ServletContextListener} to be automatically invoked.
  NOTE! Anything added here should be idempotent, i.e. there should be no problem executing the listener twice.