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diff --git a/sca-java-2.x/trunk/samples/learning-more/binding-comet/pubsub-webapp/README b/sca-java-2.x/trunk/samples/learning-more/binding-comet/pubsub-webapp/README new file mode 100644 index 0000000000..845ff70e58 --- /dev/null +++ b/sca-java-2.x/trunk/samples/learning-more/binding-comet/pubsub-webapp/README @@ -0,0 +1,102 @@ +Tuscany - Learning More - Binding Comet - PubSub Webapp +----------------------------------------------------------------- + +This sample demonstrates how Tuscany can expose services via Comet techniques +as well as how to interact with them using Tuscany's javascript toolkit. It +also demonstrates how to push multiple responses for a single request using +SCA callbacks via comet techniques. + +This project contains a component that registers browser clients' interest in a +certain event type. When an event of that type comes in, it notifies all registered +clients. The event processor exposes a service via the websocket binding which +enables server push to clients. Note that Tuscany 2.x doesn't have any conversational +support so this has to be handled at application level by passing ids back and forth +between the client and the server. + +By adding <tuscany:binding.comet/> to a service definition, the Tuscany runtime +will handle the communication between the browser client and the service +implementation using Comet techniques. This enables bidirectional communication +over HTTP, therefore enabling server push. For more information, check +http://en.wikipedia.org/wiki/Comet_(programming). + +The comet binding is using the Atmosphere Framework under the hood to acomodate +as many deployment envorinments as possible. Basically, it checks if the +application server supports Servlet 3.0 falling back to a number of native +comet solutions provided by vendors (Jetty, Tomcat, WebLogic, GlassFish and +others). If none is available, Atmosphere will fallback to blocking IO. + +In order to enable callbacks to push multiple responses, you need to declare the +CometCallback in the service definition as follows: + <interface.java interface="org.apache.tuscany.sca.sample.comet.ChatService" + callbackInterface="org.apache.tuscany.sca.binding.comet.runtime.callback.CometCallback" /> + <tuscany:binding.comet /> + <callback> + <tuscany:binding.comet /> + </callback> + +The callback object has methods that facilitate sending messages back to the +calling client. It can be injected in the service implementation using the @Callback +annotation. + +One requirement that service methods have to meet to enable multiple response +support is that they have to be annotated with @OneWay to enable non-blocking +support. Without it, methods are treated synchronously sending a single response +which is the object returned by the method call. + +Invoking comet services can be done using Tuscany's javascript API which simulates +SCA in the browser. It uses the Atmosphere jQuery plugin under the hood. In order +to use it, the following script has to be included in the client page: + <script type="text/javascript" + src="tuscany-comet-js/org.apache.tuscany.sca.CometComponentContext.js"> + </script> + +The javascript toolkit permits choosing between two comet techniques: HTTP streaming +and long polling. More detailed information about them can be found on the previously +mentioned wikipedia page. + +First, a connect operation has to be issued in order to initiate communication +with the server side using the technique of your choice. This is done using the +connection method as follows: + SCA.TuscanyComet.connect('streaming'); // for HTTP streaming + SCA.TuscanyComet.connect('long-polling'); // for long polling + SCA.TuscanyComet.connect(); // starts with HTTP streaming and falls back to long polling if necessary + +The Tuscany Comet toolkit will inject proxies for all services defined in the composite +that are using binding.comet. All invocation and connection management is handled +under the hood so in order to invoke a comet service, the following should be called: + SCA.CometComponentContext.<service name>.<operation name>(<parameters>, callback); + +The callback parameter is the function that will handle responses received for a +certain service operation. It has a single argument which is the response: + function callback(response) { + // handle response + }; + +Note that the data exchange is automatically handled by the binding, so parameters +will be mapped to the data types defined in the method definition. Also, the response +will have the same data type as the server side object used to wrap the response. +Objects are passed over the wire in JSON format. + +Another detail worth mentioning is that the binding will use a single HTTP +connection to handle communication between a browser client and all services +defined using binding.comet in the same composite. Requests and responses will get +multiplexed via the same channel and get routed to the appropriate service +implementation, respectively javascript function. This is done in order to avoid +the 2 HTTP connection limit imposed by browsers. For more info, check +http://www.openajax.org/runtime/wiki/The_Two_HTTP_Connection_Limit_Issue. + +In order to run the sample, you can execute "mvn clean install t7:run" which will +start a Tomcat 7 instance automatically or use "mvn package" and deploy the resulting +war to the application server of your choice. + +Next, point your browser at + http://localhost:8080/sample-binding-comet-chat-webapp/ + +You can now register or unregister for any of a number of events. When an event is fired +on the server side, the browser client will receive a notification which will be displayed +in the page. You can see the persistent HTTP streaming connection or long polling subsequent +connections using the developer tools provided by your browser. + +The comet binding is an experimental binding so community feedback is much +appreciated. Feel free to send comments or suggestions on the Apache Tuscany +dev mailing list (dev@tuscany.apache.org).
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