private void addTapChannel() {
		Assert.notNull(outputChannel, "Output channel can not be null.");
		Assert.notNull(messageBus, "MessageBus can not be null.");
		logger.info("creating and binding tap channel for {}", tapChannelName);
		DirectChannel tapChannel = new DirectChannel();
		tapChannel.setBeanName(tapChannelName + ".tap.bridge");
		messageBus.bindPubSubProducer(tapChannelName, tapChannel, null);
		outputChannel.addInterceptor(new WireTap(tapChannel));
	}
Add tap channel to the module's output channel.
Also, bind the tap channel to the message bus.
spring-xd-dirt/src/main/java/org/springframework/xd/dirt/plugins/spark/streaming/MessageBusSender.java