Non HTTP initiated broadcast with Atmosphere framework

In this blog post I would like to show you how you can push server side events to a web application using the atmosphere framework. I will also show how you can broadcast to a set of AtmosphereResource instances, not to all suspended connections. If you want to jump right to the code have a look at my github account.

	git clone https://github.com/altfatterz/atmosphere-fun
	cd atmosphere-fun
	mvn clean install
	mvn jetty:run

In this simple example the backend will notify the front-end about the following three events

	public enum Event {
	ACCOUNT_DEBITED, ACCOUNT_CREDITED, ACCOUNT_LOCKED
	}

In order to demonstrate the selective broadcast functionality we will broadcast ACCOUNT_DEBITED to chrome, ACCOUNT_CREDITED to firefox and ACCOUNT_LOCKED to IE browser clients. In real application you would broadcast the event to the currently logged in user whose account was debited, credited or locked.

On the front-end with the help of atmosphere.js I send as a header the information about the client (currently the type of the browser)

	var request = { url: document.location.toString() + 'event',
	contentType : "application/json",
	logLevel : 'debug',
	transport : 'websocket',
	fallbackTransport : 'long-polling' ,
	trackMessageLength : true,
	reconnectInterval : 5000,
	enableXDR: true,
	timeout : 60000,
	headers : {sessionId : sessionId} // 0 for firefox, 1 for chrome, 2 for IE
	};
	subSocket = atmosphere.subscribe(request)

The initial transport is set to websocket, however if the browser or backend doesn't support it, it will fall back transparently to long polling. The subscribe function initiates a GET request which is handled by the following managed service

	@Singleton
	@ManagedService(path = "/event")
	public class EventService {
	}

With a camel timer component we simulate the continuous event generation. The events are broadcasted to the appropriate AtmosphereResource which models a connections between a client and the server.

	BroadcasterFactory broadcasterFactory = BroadcasterFactory.getDefault();
	Broadcaster eventBroadcaster = broadcasterFactory.lookup("/event");
	Collection<AtmosphereResource> atmosphereResources = eventBroadcaster.getAtmosphereResources();
	for (AtmosphereResource atmosphereResource : atmosphereResources) {
	if (message.getSessionId().equals(getSessionId(atmosphereResource))) {
	eventBroadcaster.broadcast(message, atmosphereResource);
	}
	}

With the help of atmosphere framework the events are pushed via websocket or long-polling transport. As you can see below with IE 9 the transport will be long polling since it does not support websockets. With chrome or firefox websocket transport will be chosen.