code: private boolean isStaticResource(String uri) {
          // find extension
          int index = uri.lastIndexOf('.');
          if(index == -1) {
              return false; // no extension found
          }
  
          String currentExtension = uri.substring(index);
          
          return STATIC_RESOURCE_EXTENSIONS.contains(currentExtension);
      }
docs: Method that given a URL checks if the resources is static or not - depending on
  the request extension like .css, .js, .png etc.
  
  @param uri
  @return