mardi 22 mars 2011

Push to individual users with atmosphere framework and GWT

This is really a draft. It is just working but I'm sure there is better way to do that. Need approving from more experimented atmosphere developers.

The idea behind pushing to individual user is to assign a broadcaster with an id (you get the id from the request parameter for example) to atmosphere resource representing a user (browser). The broadcaster need to be added to the broadcaster factory. Now, at anytime you can get this broadcaster by issuing a lookup by id.

In the previous post we have seen how to setup atmosphere-gwt-demo project under Eclipse. When your run the atmosphere-gwt-demo project you get a window that shows 6 buttons: post request, poll, broadcast, open child window, send to the child window and a stop comet button.

In this post, I'll describes steps I followed to find my way to push to individual users.

The scenario is simple:

An external server send notifications as http post request with one parameter that identifies the target user, the atmosphereHandler receives the notification and send a message to the appropriate browser (The one that has login with the same id)

AtmosphereClient initialization

AtmosphereClient initialization happens in the GWT entry point

In the onModuleLoad we call the initialize() method:

public void initialize() {

        MyCometListener cometListener = new MyCometListener();

        AtmosphereGWTSerializer serializer = GWT.create(EventSerializer.class);
        // set a small length parameter to force refreshes
        // normally you should remove the length parameter
        System.out.println("Client url is "+GWT.getModuleBaseURL());
//retrieve the login from the browser GET request 
        String login ="login");
        client = new AtmosphereClient(GWT.getModuleBaseURL()+"gwtComet"+"?login="+login, serializer, cometListener);

The AtmosphereClient establish a connection with an atmosphereHandler at this url
We are using a cometListener which listens to events coming from the atmosphereHandler through the onMessage(), onHeartbeat(), onError(), etc...

I've add the login request parameter to identify each browser(user)

The server side: The atmosphereHandler

When you call client.start(), the onRequest() method of the atmosphereHandler get called

public void onRequest(AtmosphereResource resource) throws IOException {
HttpServletRequest request = resource.getRequest();

String login_key = "login";
String login_value = request.getParameter(login_key);
if(login_value != null){
    //add this broadcaster to the broadcasterFactory
    addBroadcasterToFactory(resource, login_value);

//external server request
if (request.getMethod().equalsIgnoreCase("POST")) {
 String for_key="for";
 String for_value = request.getParameter(for_key);
 if(for_value != null && for_value.length() > 0){
  System.out.println("Received a notification, going to notify user "+for_value);
  // Single Connection/Session
  Broadcaster singleBroadcaster= BroadcasterFactory.getDefault().lookup(DefaultBroadcaster.class, for_value);
  singleBroadcaster.broadcast("My first push. User "+for_value);

In this method we are trying to add a broadcaster to the BroadcasterFactory with the id of the user being login in.

In the other hand, if the request is a post (Notification from external server) we lookup the broadcaster then push something.

The addBroadcasterToFactory is as follow:

public void addBroadcasterToFactory(AtmosphereResource resource, String broadcasterID){
  Broadcaster singleBroadcaster= BroadcasterFactory.getDefault().lookup(DefaultBroadcaster.class, bdct);
  if(singleBroadcaster != null){
   resource.setBroadcaster(singleBroadcaster); //each browser opened by this user will receive the same push message
   return false;
     Broadcaster selfBroadcaster = new DefaultBroadcaster(broadcasterID);

     boolean added = BroadcasterFactory.getDefault().add(selfBroadcaster, broadcasterID);
     System.out.println("Was broadcaster added? "+added);
In this method we created a defaultBroadcaster with the broadcasterID (user id) and assign it the atmosphere resource.

Running our example:

Open a browser and enter the following url:

This browser will listen to push request.

Send notification:

Make the following post request (I used chrome with Client REST simple extension)

You should now see a notification on the client browser.

Hope this helps someone who tries to achieve the same. There may be better ways of doing this. I think I will have to use this approach until someone suggests a better solution.

vendredi 18 mars 2011

Starting with atmosphere framework, GWT and Maven under Eclipse

Months ago i was searching for a push solution to integrate to my web applications and I discovered Atmosphere, a nice framework, developed by nice people.

Latest version of Atmosphere is 0.8. Project is growing fast and development is intensive.

In this post, I want to summarize steps I followed to get atmosphere-gwt-demo working.

I use Eclipse Helios (3.6 SR2), I've already Maven plugin installed (m2eclipse), and google-eclipse-plugin (even if this one will not be used for the purpose of this article)

Download atmosphere project:

git clone

Wait few minutes for download to complete then go to eclipse and import the entire project as a maven project.

Fix some maven properties:

Go to atmosphere-gwt-demo, we'll be editing the pom.xml. Locate the declaration of gwt-maven-plugin (see the complete configuration) and add

Without this line, maven will not copy files located under src/main/META-INF/ (Most important atmosphere.xml) and the application will not work.

For more information see:

Install dependencies:

Now, if you try to run the demo, you will get errors. This happens because you didn't install atmosphere runtime dependencies.

For each error (missing class), find its containing sub-project, right click on it -> run as ... -> maven install

Run the demo:

Right click on atmosphere-gwt-demo -> Run as -> Maven build ... and enter in the goal field: gwt:run

Wait few seconds for the embedded jetty server to start and load your application, then open the hosted mode url into your favorite browser (I use Google Chrome with the GWT plugin installed).

Debug atmosphere-gwt-demo

This post shows how to debug a GWT application with the gwt-maven-plugin.

I just changed the port from 8000 to 8001 because for some reason this port was already in use (I think eclipse uses it)

Add the following line to the gwt-maven-plugin configuration in pom.xml of atmosphere-gwt-demo


Right click on atmosphere-gwt-demo->Run As->Maven build ...
In the following dialog, enter "gwt:debug" as goals, save it.

Click on the dropdown of the debug button on the toolbar, select "Debug Configurations".

In the left panel, find “Remote Java Application”, select it and click the icon for "New launch configuration" (top left corner). Accept defaults, save, and close.

Now, you are ready, start the debug server by running the debug launcher we just created. (the one with goal gwt:debug). When you see "Listening for transport dt_socket at address: 8001" in the console output, run the attach launcher we just created (the remote debugger).

Finally, here is the complete gwt-maven-plugin