code: public Set<WebSocketChannel> getChannels(String uri) {
          Objects.requireNonNull(uri, Required.URI.toString());
  
          final Set<WebSocketChannel> channels = this.cache.get(Default.WSS_CACHE_PREFIX.toString() + uri);
  
          return (channels == null) ? new HashSet<>() : channels;
      }
docs: Retrieves all channels under a given URL
  
  @param uri The URI resource for the channels
  
  @return A Set of channels for the URI resource