But it seems there is no support for "customized message buses" in the Liferay 7.

Blatantly false statement.

There are some pre-configured message buses in Liferay 7 which though cannot be customized to this particular need.

Well, you shouldn't really change Liferay's own bus listeners as you may break functionality the portal relies on.

It seems integrating a messaging bus system (like activeMQ etc.) would be an overkill and that is the reason we relied on Message Buses.

This is likely true. The LMB is a light-weight server side framework and not a full-blown MQ, but that lightness is often enough to get the job done.

Now if we take out the false assumptions, I think your post would have been better received had it actually been:

I would like to do some custom Liferay Message Bus messaging, but I haven't found any documentation on it after searching dev.liferay.com. Is this still supported and, if so, how would I do it?

Good question. Yes the message bus is still there, it is still supported and is still doable even under OSGi. I'm sorry the doco support isn't there, I'll see if I can raise it as an issue with the docs team.

There are two key parts for using the LMB; you need a listener and you need a sender.

For the listener, you can implement pretty much like:

@Component(
	immediate = true, property = {"destination.name=MyEchoDestination"},
	service = MessageListener.class
)
public class EchoMessageListener extends BaseMessageListener {

	@Override
	protected void doReceive(Message message) throws Exception {
		if (_log.isInfoEnabled()) {
			_log.info("Received: " + message);
		}

		String payload = (String)message.getPayload();

		if (_log.isInfoEnabled()) {
			_log.info("Message payload: " + payload);
		}

		String responseDestinationName = message.getResponseDestinationName();

		if ((responseDestinationName != null) &&
			(responseDestinationName.length() > 0)) {

			Message responseMessage = new Message();

			responseMessage.setDestinationName(responseDestinationName);
			responseMessage.setResponseId(message.getResponseId());

			//This is just for demo purposes

			responseMessage.setPayload(payload);

			_messageBus.sendMessage(
				message.getResponseDestinationName(), responseMessage);
		}
	}

	private static final Log _log = LogFactoryUtil.getLog(
		EchoMessageListener.class);

	@Reference
	private volatile MessageBus _messageBus;
}

For OSGi, this will result in registering a MessageListener instance for the destination defined in the properties.

The next part you need is the message sending code:

@Component(
	immediate = true,
	property = {
		"com.liferay.portlet.display-category=category.sample",
		"com.liferay.portlet.instanceable=true",
		"javax.portlet.display-name=Echo Portlet",
		"javax.portlet.init-param.template-path=/",
		"javax.portlet.init-param.view-template=/view.jsp",
		"javax.portlet.resource-bundle=content.Language",
		"javax.portlet.security-role-ref=power-user,user"
	},
	service = Portlet.class
)
public class EchoPortlet extends MVCPortlet {

	...

	public void sendMessage(
		ActionRequest actionRequest, ActionResponse actionResponse) {

		if (_log.isInfoEnabled()) {
			_log.info("Sending message to DE Echo service");
		}

		Message message = new Message();

		message.setDestinationName("MyEchoDestination");
		message.setPayload("Hello World!");
		message.setResponseDestinationName("MyEchoResponse");

		_messageBus.sendMessage(message.getDestinationName(), message);
	}

	private static final Log _log = LogFactoryUtil.getLog(EchoPortlet.class);

	@Reference
	private MessageBus _messageBus;
}

That should get you there. Note that you're responsible for the MyEchoResponse listener









Come meet me at 2017 LSNA!

Same here into Liferay 7.1.2 doReceive method is not calling ???and how can we call by changing Impl class???