Problems with Push support in Vaadin

Question

I'm having some serious issues with the Server Push support in Vaadin 7, and it's proving difficult to pin down the problem. I've followed all the steps in the Book of Vaadin on enabling server push, including adding the vaadin-push.jar file to WEB-INF/lib, adding the "asyncSupported = true" parameter to the @WebServlet annotation, and adding the @Push annotation to the UI class. (I've also tried specifying the equivalent in the deployment descriptor.) I also added the org.atmosphere.useWebSocketAndServlet3=true property to the catalina.properties file of my Tomcat 7 server, as suggested in https://vaadin.com/wiki/-/wiki/Main/Working%20around%20push%20issues.

I found the Server Push support to be very quirky, making it difficult to identify the problem. For instance, when developing code, the server will often not automatically re-start; only recognizing new code when I close the browser (not just the browser window), stop the server and re-start Eclipse; missing any of these steps will result in the Server Push not working. Note that this issue only occurs when Server Push is enabled. I read something about sessions not expiring when push is enabled (https://vaadin.com/forum#!/thread/3576361), so maybe that's the reason..

I often encounter suspicious log messages:

Mar 02, 2014 9:25:45 PM com.vaadin.server.communication.PushHandler$3 run
WARNING: Could not find push connection to close: 38450652-2a2b-4221-8300-8313e9c4779a with    
transport WEBSOCKET

Mar 02, 2014 9:25:45 PM org.apache.catalina.loader.WebappClassLoader loadClass
INFO: Illegal access: this web application instance has been stopped already.  Could not load     
java.nio.ByteBuffer.  

It does seem that the Atmosphere is finding the async support:

INFO: Atmosphere is using async support:     
org.atmosphere.container.Tomcat7AsyncSupportWithWebSocket running under container: Apache     
Tomcat/7.0.47

I also found this error; don't know whether it indicates a serious problem (haven't tried resolving it, since I don't want to get into the Atmosphere stuff):

WARNING: No BroadcasterCache configured. Broadcasted message between client reconnection will be 
LOST. It is recommended to configure the org.atmosphere.cache.UUIDBroadcasterCache

That said, Firefox works quite well with the Server Push, while Chrome has problems and IE spews errors (surprise!). In particular, Chrome often takes quite a while to communicate a UI interaction (e.g., button push) to the server, whereby a spinner (changing color from yellow to orange to red) appears at the right top. IE simply updates the wrong UI components when multiple windows are open. So, as long as every user employs Firefox there's no problem, but I can't possibly assume that.

I came across this post, where developers vented their frustration on the feature: https://vaadin.com/forum#!/thread/4040408. This is quite a recent post, so it doesn't sound too promising.. The only reason I need the Server Push feature is to allow the ChatBox add-on (https://vaadin.com/directory/-/directory/addon/chatbox) to update in real-time.

Any ideas? Has anyone gotten these kinds of errors and managed to get some workaround? Or even better, has anyone gotten the ChatBox add-on to work with the Server Push?

Thanks,

William

Answer 1

Try Again

Web Push is still a young technology, especially the WebSocket variety. Tomcat for example replaced one WebSocket implementation with another. Vaadin’s adoption of the Atmosphere library and all the other work in Vaadin 7 are relatively new. Much has improved in the months following the posting of this Question. I suggest giving Push another try.

Use the latest versions of your web server. For example, both Tomcat 7 & 8 and Jetty have made significant changes in their support of Push and WebSocket.

Use the latest version of Java 8 and Vaadin (7.3.7 now).

No Need For setPollInterval

No need to call UI::setPollInterval as was mentioned in the comments above. That feature uses only one approach to Push.

All you need is the @Push annotation. And a Thread, or better, a ScheduledExecutorService to update the data for display in your app. Using the @Push annotation engages the Atmosphere library. Atmosphere tries multiple techniques of Push, starting with WebSocket, and automatically uses other techniques as a fall-back.

Working Example

I recently (2015-01) posted a working example of Push working in Vaadin 7.3.7 as an answer to another question. My example is purposely minimal, using a single file to replace the MyUI file’s content in a new default Vaadin app project.