code: protected SubscriptionSummary postNotification(final Subscriber subscriber, final String mimeType, final byte[] payload) {
          final SubscriptionSummary result = new SubscriptionSummary();
  
          try {
              final URL target = new URL(subscriber.getCallback());
              LOG.info("Posting notification to subscriber {}", subscriber.getCallback());
              result.setHost(target.getHost());
  
              final HttpURLConnection connection = (HttpURLConnection) target.openConnection();
              connection.setRequestMethod("POST");
              connection.setRequestProperty("Content-Type", mimeType);
              connection.setDoOutput(true);
              connection.connect();
  
              final OutputStream os = connection.getOutputStream();
              os.write(payload);
              os.close();
  
              final int responseCode = connection.getResponseCode();
              final String subscribers = connection.getHeaderField("X-Hub-On-Behalf-Of");
              connection.disconnect();
  
              if (responseCode != 200) {
                  LOG.warn("Got code {} from {}", responseCode, target);
                  result.setLastPublishSuccessful(false);
                  return result;
              }
  
              if (subscribers != null) {
                  try {
                      result.setSubscribers(Integer.parseInt(subscribers));
                  } catch (final NumberFormatException nfe) {
                      LOG.warn("Invalid subscriber value " + subscribers + " " + target, nfe);
                      result.setSubscribers(-1);
                  }
              } else {
                  result.setSubscribers(-1);
              }
          } catch (final MalformedURLException ex) {
              LOG.warn(null, ex);
              result.setLastPublishSuccessful(false);
          } catch (final IOException ex) {
              LOG.error(null, ex);
              result.setLastPublishSuccessful(false);
          }
  
          return result;
      }
docs: POSTs the payload to the subscriber's callback and returns a SubscriptionSummary with
  subscriber counts (where possible) and the success state of the notification.
  
  @param subscriber subscriber data.
  @param mimeType MIME type for the request
  @param payload payload of the feed to send
  @return SubscriptionSummary with the returned data.