![Wire Protocol • FIN • Indicates the last frame of a message • RSV[1-3] • 0, or extension-specific • OPCODE • Frame identifier (continuation, text, close, etc) • MASK • Whether the frame is masked • PAYLOAD LEN • Length of data • PAYLOAD DATA • Extension Data + Application Data](https://image.slidesharecdn.com/kcdc-async-final-slideshare-130508150355-phpapp01/75/Asynchronous-Web-Programming-with-HTML5-WebSockets-and-Java-33-2048.jpg)
Uploaded byJames Falkner
Asynchronous Web Programming with HTML5 WebSockets and Java
The document provides an overview of asynchronous web programming using HTML5 WebSockets and Java, focusing on execution models and programming paradigms such as event-driven and threaded models. It discusses the benefits of non-blocking I/O, frameworks, and Java EE features for managing asynchronous tasks and WebSockets. The content includes examples of event-driven programming in Java and the implementation of WebSocket connections in client-server architectures.
Asynchronous Web Programming with HTML5 WebSockets and Java
- 1. Asynchronous Web Programming withHTML5 WebSockets and Java James Falkner Community Manager, Liferay, Inc. james.falkner@liferay.com @schtool
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- 3. The Asynchronous Word •Literally: Without Time • Events that occur outside of the main program execution flow • Asynchronous != parallel/multi-threading
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- 5. Execution Models Single-Threaded SynchronousModel • Not much to say here
- 6. Execution Models Threaded Model •CPU controls interleaving • Developer must coordinate threads/processes • “preemptive multitasking”
- 7. Execution Models Asynchronous Model •Developer controls interleaving • “cooperative multitasking” • Wave goodbye to race conditions, synchronized, and deadlocks! • Windows 3.x, MacOS 9.x, Space Shuttle
- 8. Execution Models The greencode (your code!) runs uninterrupted until it (you!) reaches a “good stopping point” (I/O)
- 9. What does thisbuy me? NOTHING! Except when • Task Pool is large • Task I/O >> Task CPU • Tasks mostly independent … Like web servers
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- 12. Threaded vs. Event-Driven while(true) { client = accept(80); /* blocked! */ new Thread(new Handler(client)).start(); } vs. new Server(80, { onConnect: { handler.handle(client); } }); /* no blocking here, move along */
- 13. Threaded vs. Event-Driven •Both can solve the exact same set of problems • In fact, they are semantically equivalent • Threaded costs in complexity and context switching • Event-Driven costs in complexity and no context switching
- 14. Forces • When toconsider event-driven, asynchronous programming models?
- 15. Async/Eventing Support • Hardware/OS:Interrupts, select(), etc • Languages: callbacks, closures, futures, promises, Reactor/IOU pattern • All accomplish the same thing: do this thing for me, and when you’re done, do this other dependent thing • Frameworks • Makes async/event programming possible or easier • JavaEE, Play, Vert.x, Cramp, node.js, Twisted, …
- 16. Reducing Complexity • Useestablished patterns • Use established libraries and tooling https://github.com/caolan/async
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- 18. Event-Driven Java/JavaEE • Java1.0: Threads and AWT • Java 1.4: NIO (Non-blocking I/O, nee New I/O) • J2EE 1.2: JMS • JavaEE 6: @Asynchronous and CDI JavaEE 7: WebSockets • Future: Lambda Expressions (closures) myButton.addActionListener(ae -> { System.out.println(ae.getSource()); });
- 19. Early Event-Driven Java •Closure-like listeners (e.g. addActionListener(), handlers) • Captured “free” variables must be final • Hogging CPU in listener is bad • References to this and OuterClass.this
- 20. Event-Driven JavaEE • Servlet3.0 • Async servlets • JAX-RS (Jersey) • Client Async API (via Futures/callbacks) • Server Async HTTP Requests • JMS • Message Redelivery, QoS, scalability, … • CDI/EJB • Via @Inject, @Asynchronous and @Observes
- 21. JavaEE Example: Event Definition publicclass HelloEvent { private String msg; public HelloEvent(String msg) { msg = msg; } public String getMessage() { return message; } }
- 22. JavaEE Example: Event Subscriber @Stateless publicclass HelloListener { @Asynchronous public void listen(@Observes HelloEvent helloEvent){ System.out.println("HelloEvent: " + helloEvent); } }
- 23. JavaEE Example: EventPublish @Named("messenger”) @Stateless public class HelloMessenger { @Inject Event<HelloEvent> events; public void hello() { events.fire(new HelloEvent("from bean " + System.currentTimeMillis())); } } <h:commandButton value="Fire!" action="#{messenger.hello}"/>
- 24. JavaEE Example: AsyncServlet
- 25. JavaEE Example: AsyncServlet
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- 27. Event-Driven JavaScript • Notjust for the browser anymore • It’s cool to like it! (again) • Language features greatly aid event-driven programming • Many, many frameworks to aid in better design
- 28. The Asynchronous Web •Goal: Responsive, Interactive sites • Technique: Push or Pull • First: Pull • Request/Response • AJAX Pull/Poll • Now: Push • Long Polling • Proprietary (e.g. Flash) • Server-Sent Events (nee HTTP Streaming) • WebSockets
- 30. WebSockets • Bi-directional, full-duplexTCP connection • Asynchronous APIs • Related Standards • Protocol: IETF RFC 6455 • Browser API: W3C WebSockets JavaScript API • Client/Server API: JSR-356 (Java) • 50+ Implementations, 15+ Languages • Java, C#, PHP, Python, C/C++, Node, …
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- 33. Wire Protocol • FIN •Indicates the last frame of a message • RSV[1-3] • 0, or extension-specific • OPCODE • Frame identifier (continuation, text, close, etc) • MASK • Whether the frame is masked • PAYLOAD LEN • Length of data • PAYLOAD DATA • Extension Data + Application Data
- 34. WebSockets Options • Endpointidentification • Version negotiation • Protocol Extensions negotiation • Application Sub-protocol negotiation • Security options
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- 36. Java Server API(JSR-356) • Endpoints represent client/server connection • Sessions model set of interactions over Endpoint • sync/async messages • Injection • Custom encoding/decoding • Configuration options mirror wire protocol • Binary/Text • PathParam • Extensions
- 37. Java Server API @ServerEndpoint("/websocket") publicclass MyEndpoint { private Session session; @OnOpen public void open(Session session) { this.session = session; } @OnMessage public String echoText(String msg) { return msg; } @OnClose … @OnError … public void sendSomething() { session.getAsyncRemote() .sendText(“Boo!”); }
- 38. Client API (JavaScript) varws = new WebSocket('ws://host:port/endpoint'); ws.onmessage = function (event) { console.log('Received text from the server: ' + event.data); // do something with it }; ws.onerror = function(event) { console. log("Uh oh"); }; ws.onopen = function(event) { // Here we know connection is established, // so enable the UI to start sending! }; ws.onclose = function(event) { // Here the connection is closing (e.g. user is leaving page), // so stop sending stuff. };
- 39. Client API (Other) •Non-Browser APIs for C/C++, Java, .NET, Perl, PHP, Python, C#, and probably others WebSocket webSocketClient = new WebSocket("ws://127.0.0.1:911/websocket", "basic"); webSocketClient.OnClose += new EventHandler(webSocketClient_OnClose); webSocketClient.OnMessage += new EventHandler<MessageEventArgs>(webSocketClient_OnMessage); webSocketClient.Connect()); webSocketClient.Send(“HELLO THERE SERVER!”); webSocketClient.Close();
- 40. Browser Support • Yourusers don’t care about WebSockets • Fallback support: jQuery, Vaadin, Atmosphere, Socket.IO, Play, etc
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- 44. WebSocket Gotchas • UsingWebSockets in a thread-based system (e.g. the JVM) • Sending or receiving data before connection is established, re-establishing connections • UTF-8 Encoding • Extensions, security, masking make debugging more challenging
- 45. WebSocket Issues • EphemeralPort Exhaustion • Evolving interfaces • Misbehaving Proxies
- 46. Acknowledgements http://cs.brown.edu/courses/cs168/f12/handouts/async.pdf (Execution Models) http://www.infosecisland.com/blogview/12681-The-WebSocket-Protocol-Past-Travails-To-Be-Avoided.html(problems) http://lucumr.pocoo.org/2012/9/24/websockets-101/ (more problems) http://wmarkito.wordpress.com/2012/07/20/cdi-events-synchronous-x-asynchronous/ (cdi examples) http://blog.arungupta.me/2010/05/totd-139-asynchronous-request-processing-using-servlets-3-0-and-java-ee-6/ (async servlets) http://vertx.io (vert.x example) https://cwiki.apache.org/TUSCANYWIKI/develop-websocket-binding-for-apache-tuscany.html (handshake image) http://caniuse.com/websockets (browser compat graph)
- 47. Asynchronous Web Programming withHTML5 WebSockets and Java James Falkner Community Manager, Liferay, Inc. james.falkner@liferay.com @schtool