Sending PubSub Messages Between Gadgets and Portlets

The Portal Directory hook required for the portlet-to-gadget tutorial is available here: –>

Have you ever wanted your gadgets to communicate with each other or with portlets? You can do so with PubSub. PubSub is implemented in Liferay to facilitate interaction between gadgets and interaction between gadgets and portlets. PubSub is a diverse messaging system that allows messages to be sent in the following manner:

  • gadget to gadget
  • portlet to gadget or vice versa
  • portlet to portlet

With the use of PubSub, the worlds of gadgets and portlets blend together, facilitating their ability to communicate and interact with each other.

We’ll run through a tutorial for gadget to gadget communication, and then show an example for using gadget to portlet communication; both will integrate Google Maps into Liferay Portal. After we’ve run through the exercises, we’ll briefly analyze specific code fragments that made the PubSub messaging possible. Let’s get started!

Communicating Between Gadgets

For gadget to gadget communication, two independent gadgets are placed on a page and configured with PubSub; these two gadgets are able to communicate with one another and provide tools that the user could not otherwise produce. As an example, we’ll demonstrate two Google Maps gadgets that publish and subscribe to the same channel. Using PubSub, these gadgets work together to display an address on a map.

The first gadget represents a publisher that enables the user to input a specific address and publish the address. The second gadget represents the subscriber who receives the address, displays the address, and locates the address on Google Maps.

Figure 1: Gadgets like Googles Address and Map gadgets are automatically synced to communicate with each other.

Figure 1: Gadgets like Google's *Address* and *Map* gadgets are automatically synced to communicate with each other.

Once the Update button is selected in the Google Address gadget, the address is published to a specific channel. Since the Google Map gadget is subscribed to that same channel, it receives the address and then displays it in the map.

Figure 2: After inputting a custom address in the Google Address gadget, you are able to see its physical location in the Google Map gadget.

Figure 2: After inputting a custom address in the Google Address gadget, you are able to see its physical location in the Google Map gadget.

That’s all there is to it! The gadgets are communicating well with each other. This simple tutorial demonstrated two gadgets communicating with each other using PubSub.

We will now dive into the source code and analyze how this interaction is accomplished. To view the full contents of the Google Map, visit the GoogleMapsPublisher.xml file.

The following excerpt from the Google Map XML file enables the gadget to use PubSub and specifies the channel (topic) to which the gadget publishes:

<Require feature="pubsub-2">
	<Param name="topics">
		    title="Google Map"

Notice the opening <Require feature="pubsub-2">, mandating the pubsub-2 feature for the gadget. The <Param name="topics"> section establishes the topic com.liferay.opensocial.gmapsdemo that the gadget publishes to. Within the topics parameter, you define all the topics your gadget uses for communication. Furthermore, the publish="true" attribute specifies the gadget’s role as a publisher to the topic.

In the JavaScript of the gadget’s content, the gadget publishes to the topic with the following invocation:

gadgets.Hub.publish("com.liferay.opensocial.gmapsdemo", address);

When the user clicks the gadget’s Update button, the message is sent by the publishing gadget to the topic named com.liferay.opensocial.gmapsdemo; PubSub broadcasts the message received on that topic to all subscribers, such as your Google Address gadget. Each subscriber receives and processes the message. In the case of your Google Map gadget, the message containing an address is processed by the gadget to show the address location on its map.

Next, we’ll analyze the tutorial’s subscribing gadget’s source code specified in the GoogleMapsViewer.xml file.

The subscriber source code is similar to that of the publisher: it mandates the pubsub-2 feature for the gadget and specifies com.liferay.opensocial.gmapsdemo as one of its topics, as you would expect; of course, the only difference is the fact that this gadget subscribes to the topic, hence the attribute setting subscribe="true".

The following JavaScript from the gadget’s content registers a callback on the com.liferay.opensocial.gmapsdemo topic:

gadgets.HubSettings.onConnect = function(hub, suc, err) {
        gadgets.Hub.subscribe("com.liferay.opensocial.gmapsdemo", callback);

The gadgets.HubSettings.onConnect function is called by the OpenSocial container, once the gadget connects to the PubSub messaging hub. In our example, the gadget subscribes to the previously mentioned topic; all subscribers to this topic receive messages sent to it.

When a message is received, the gadget’s callback() function is executed. In this example the callback method sends the received message (the address sent by the publisher), calls google.maps.Geocoder.geocode() to get the locations, and finally processes and displays the locations on the map.

In summary, subscriber gadgets need to specify a topic and register a callback function on that topic to handle the messages they receive.

As you can see, PubSub allows your site to run efficiently and enables otherwise unconnected gadgets to communicate and flourish within Liferay Portal.

Gadgets are not limited to only communicating with other gadgets. In the next section, we will demonstrate the capabilities of communication between portlets and gadgets.

Communicating Between Portlets and Gadgets

For this tutorial, we’ll continue exploring the Google Map gadget inside of Liferay. If you have portlet applications that can take advantage of the functionality your Maps gadgets have to offer, it would certainly be convenient for a user to allow communications between those gadgets and your portlets.

As a demonstration, we’ll show a customized Portal Directory portlet that communicates to the Google Map gadget using PubSub. For each user listed in the Portal Directory portlet that has a specified address, a Show in Google Maps link is displayed beneath the user’s address. When the link is selected, the location of the user’s address is displayed in the Google Map gadget.

Figure 3: The modified Portal Directory portlet sends the users address to the Google Map gadget to display.

Figure 3: The modified Portal Directory portlet sends the user's address to the *Google Map* gadget to display.

The Portal Directory portlet’s addresses.jsp file was edited to assign the portlet as a PubSub publisher, but what edits to the JSP file made this possible?

As you know from explanations given earlier, the Google Map gadget is distinguished as a subscriber. Therefore, the Portal Directory portlet needed to take on the publisher role to enable communication. To enable the Portal Directory portlet to publish to the topic on which the Google Map gadget is subscribed, we inserted the following JavaScript into the addresses.jsp file:

<script type="text/javascript">
	function publishAddress(address) {'gadget:com.liferay.opensocial.gmapsdemo', address);

This code involves a publishAddress() function that’s called whenever you click on the Show in Google Maps link. The function invokes the function, passing in the name of the channel receiving the message and the user’s address as the message. One thing to note is that when a portlet sends data to a gadget, there must be a gadget: prefix before the channel declaration; this distinguishes who the messages are intended for when they are broadcast across a channel.

Notice that you don’t need to change anything for your Google Map gadget, since it’s already subscribed to that channel; you only needed to define the Portal Directory portlet as a publisher to that channel.

Lastly, a button is needed to initiate the publishing of the address to the topic in the Portal Directory portlet; to do this, we inserted the following into the addresses.jsp file:

<a href="javascript:void(0);" onclick='publishAddress("<%= street1 + ", " + zipCode + ", " + city %>")'>Show in Google Maps</a>

Letting your portlets communicate with gadgets enhances your portlet applications and gives you a plethora of different ways you can enhance your user’s experience.

Using Liferay’s Message Bus

Customizing Liferay Portal with Hooks

User Interfaces with AlloyUI


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