Developing Revolutionary Web Applications using Comet and Ajax Push

Developing Revolutionary Web Applications using Comet and Ajax Doris Chen Ph.D. Staff Engineer/Technology Evangelist 1

Agenda • Web 2.0 • Introduction to Comet • Asynchronous HTTP and the Server • Develop a Slideshow Chat Application using Cometd (demo) • Develop a Two Player Game using Comet (demo) • Future, Summary and Resources 2

Web 2.0 A Web by the people, for the people. Documents on the web increasingly generated by users Out of the Information Age, into the Participation Age Are web user interfaces becoming more powerful? Is the user an HTTP client? 3

The Asynchronous Web Revolution The Web enters the Participation Age. • Ajax is still typically synchronous with user events • Full asynchrony has updates pushed from server any time > Update pages after they load > Send users notifications • Allow users to communicate and collaborate within the web application • Called “Ajax Push”, “Comet”, or “Reverse Ajax” > This is the full realization of Ajax, now fully asynchronous 4

Applications in the Participation Age Application-mediated communication. • Distance learning • Collaborative authoring • Auctions • Shared WebDAV filesystem • Blogging and reader comments • SIP-coordinated mobile applications • Hybrid chat/email/discussion forums • Customer assistance on sales/support pages • Multi-step business process made collaborative • Shared trip planner or restaurant selector with maps • Shared calendar, “to do” list, project plan • Games 5

Server-mediated Collaboration External Application Server User • User Initiated Push Push Action • Application Initiated Client 1 Client 2, 3, ..n 7

What is Comet (Ajax Push)? Responsive, low-latency interaction for the web • A programming technique that enables web servers to send data to the client without having any need for the client to request for it • Allows creation of highly responsive, event- driven web applications > Keep clients up-to-date with data arriving or changing on the server, without frequent polling • Pros > Lower latency, not dependent on polling frequency > Server and network do not have to deal with frequent polling requests to check for updates 8

Ajax Poll vs Ajax Push Bending the rules of HTTP. • Comet Refers to both the Long Polling and Streaming methods of web programming 9

Ajax Poll vs Ajax Push Bending the rules of HTTP. • Poll: > Send a request to the server every X seconds > The response is “empty” if there is no update • Long Poll: (most popular, demo use) > Send a request to the server, wait for an event to happen, then send the response > The response is never empty • Http Streaming: > Send a request, wait for events, stream multi- part/chunked response, and then wait for the events > The response is continually appended to 10

Comet Examples • GMail and GTalk • Meebo • 4homemedia.com (using GlassFish project's Comet) • JotLive • KnowNow • Many more … 11

Agenda • Web 2.0 • Introduction to Comet • Asynchronous HTTP and the Server • Develop a Slideshow Chat Application using Cometd (demo) • Develop a Two Player Game using Comet (demo) • Summary and Resources 12

How Push works Keep an open connection. • Deliver data over a previously opened connection • Always “keep a connection open” > do not respond to the initiating request until event occurs • Streaming is an option > send response in multiple parts without closing the connection in between 13

Server Architecture Challenge Can Push scale? • Using blocking, synchronous technology will result in a blocked thread for each open connection that is “waiting” > Every blocked thread will consume memory > This lowers scalability and can affect performance • To get the Java Virtual Machine (JVM™) to scale to 10,000 threads and up needs specific tuning and is not an efficient way of solving this • Servlets 2.5 are an example of blocking, synchronous technology 14

Architecture Challenges The serious effect of blocking threads (default thread stack size) 15

Technology Solution NIO avoids blocked threads. • Use new I/O (NIO) non-blocking sockets to avoid blocking a thread per connection • Use technology that supports asynchronous request processing > Release the original request thread while waiting for an event > May process the event/response on another thread than the original request • Advantages > Number of clients is primarily limited by the number of open sockets a platform can support > Could have all clients (e.g. 10’000) “waiting” without any threads processing or blocked 16

Server-side Ajax Push: Who supports what The asynchronicity matrix Container Asynchronous IO Suspendible Delivery Request/ Guarantee Response Jetty X Tomcat X X GlassFish X X X Resin X WebLogic X 17

HTTP modules • The Grizzly Framework also have an HTTP framework that can be used to build Web Server > This is what GlassFish™ v1|2|3 build on top of. > More specialized modules are also available like Comet (Async HTTP). • Simple interface to allow customization of the HTTP Protocol > GrizzlyRequest: A utility class to manipulate the HTTP protocol request. > GrizzlyResponse: A utility class to manipulate the HTTP protocol response. > GrizzlyAdapter: A utility class to manipulate the HTTP request/response object. 18

Introduction to GlassFish Grizzly Comet • Grizzly Comet is a framework that ship with GlassFish v1|2|3, and can also be embedded into any application using the Grizzly Embedded interface (no GlassFish involved) • The Grizzly Comet Framework includes a set of components that can be used for building Comet based application: > Grizzly Comet Framework, Continuation, Grizzlet, Messages Bus, Bayeux support 19

Grizzly Comet Components Grizzlet Bayeux Continuation Messages Bus Grizzly Comet Framework Grizzly HTTP Grizzly NIO Framework 20

Asynchronous Ajax Demo Grizzlet with Project jMaki on GlassFish 21

What Is Cometd? • HTTP-based event routing bus using > Bayeux Protocol > Comet as underlying push technologyl • Consists of a protocol spec called Bayeux, JavaScript technology libraries (DOJO toolkit), and an event router • The Server uses async techniques to “park” the request without blocked threads • Comet programming is easy, cometd is even easier > No server-side elements need to be created 23

Grizzly Comet Components Grizzlet Bayeux Continuation Messages Bus Grizzly Comet Framework Grizzly HTTP Grizzly NIO Framework 24

What Is the Bayeux Protocol? • Bayeux is a negotiated, multi-transport, JSON-based protocol for publish/subscribe asynchronous messaging between: > Web browser and server, Server and web browser > Web browser and web browser > http://svn.xantus.org/shortbus/trunk/bayeux/bayeux.html • Part of the Dojo Cometd project > http://cometdproject.dojotoolkit.org/ • Multiple server implementations > JavaScript programming language, Java™ programming language, perl, python 25

Bayeux/Cometd JSON Publish/Subscribe [ { "channel": "/some/name", "clientId": "83js73jsh29sjd92", "data": { "myapp" : "specific data", value: 100 } } ] • JSON Messages are published on specified channels • Channel operations: connect, subscribe, unsubscribe, etc. • Multiple transports: polling, long-polling, iframe, flash • Server-side reflector with no server-side application possible 26

Software and Configuration • Glassfish Application Server (V2 or V3 TP2) > Needs to be enabled for Comet ● Configure using GlassFish V2 admin console ● Configure in NetBeans + for GlassFish V3 ● or Command line – asadmin set server.http-service.http-listener.http-listener- 1.property.cometSupport=true ● or Edit domain.xml in GlasFish – <http-listener id="http-listener-1" port="8080"><property name="CometSupport" value="true" /> • Grizzly Comet APIs • A browser Client, running Javascript, support Ajax 27

GlassFish V3 Comet Enable (in NetBeans) 28

Enable Comet in GlassFish V2 Admin Console 29

Enabling Bayeux in GlassFish • Configure web.xml web.xml <servlet-mapping> <servlet-name>Grizzly Cometd Servlet</servlet- name> <url-pattern>/cometd/*</url-pattern> </servlet-mapping> 30

Step1 : Initialize Comet Server dojo.require("dojox.cometd"); //Initialize a connection to the given Comet server: the GlassFish Grizzly Bayeux servlet dojox.cometd.init("serverURL"); 31

Step 2: Subscribe dojox.cometd.subscribe(“topic”, "remote topic", "callbackFunction"); Comet Server • Subscribes the client to the topic channel • Any time a message is sent to the topic channel the callback will be invoked Client 2 Client 1 32

Step 3: Publish JSON message dojox.cometd.publish("topic", {slide: url}); Comet Server a client publishes the next slide url to the topic channel new slide url client 1 33

Step 4: Update Clients: CallBack Invoke Comet Server callBackFunction(slideUrl){ slide.innerHTML ="<img src='" + slideUrl + "'/>"; ... } Update Browser ●The callback function is Update Browser called with the published message when a new message is received ●This callback function updates the browser content ● html img tag with the slide url from the Client 2 Client 3 published message 34

Slideshow Chat Demo 35

Grizzly Comet Framework • The Framework contains the classes required to add support for Comet in a Web Application • Main classes to interact with (details next): > CometEngine > CometContext > CometHandler > NotificationHandler > CometReader > CometWriter 37

Grizzly Comet Framework How it works send CometHandler CometHandler Browser 1 CometHandler CometContext filters push Browser 2 send Push data NotificationHandler Servlet Database ClusterCometHandler 38

Grizzly Comet in Steps • Suspend: > addCometHandler(CometHandler) • Push: > notify(<? extends Object>) // All suspended responses > notify(<? extends Object>, CometHandler) // Only one • Write: Inside CometHandler.onEvent() > PrintWriter.write(CometEvent.attachment()); • Resume: > resumeCometHandler(CometHandler) 39

CometContext • A CometContext is a distribution mechanism for pushing messages that are delivered to multiple subscribers called CometHandler (a la JMS Queue/Topic) • All http response registered to a CometContext automatically becomes suspended, waiting for an event (a push) to happens • A browser receives only those messages published after the client suspend its response via CometContext 40

Grizzly Comet Framework • CometHandler > A CometHandler contains the business logic of what will be pushed back to the browser > A CometHandler might be invoked by the Container: ● When a push operation happens ● When a I/O operations are ready to be process (asynchronous read or write) ● When the browser close the connection 41

Grizzly Comet Framework (cont.) • NotificationHandler > An inside object that you will decide to what to do with the push operation: ● Throttle: if too many push occurs simultaneously, should we delay them? ● Aggregate: should we cache push operations and aggregate them to avoid overloading the network? ● Filter: should all messages by pushed back to the client? ● Should a thread pool be used to improve the push operation? Should a JMS backed be used to deliver the message? > The DefaultNotificationHandler push all messages 42

Four Simple Steps for Comet • Step 1: Initialize Comet • Step 2: Define your CometHandler • Step 3: Connect to Comet Servlet: Add CometHandler to CometContext • Step 4: Advertise changes • Step 5: More details on Client 43

Step 1: Initialize Comet Register a CometContext //In TTTComet Servlet class... public void init(ServletConfig config) { ServletContext context = config.getServletContext(); contextPath = context.getContextPath() + "/TTTComet1"; CometEngine engine = CometEngine.getEngine(); CometContext cometContext = engine.register(contextPath); cometContext.setExpirationDelay(120 * 1000); //All connections registered to a CometContext automatically becomes suspended, waiting for an event (a push) to happen //A browser receives only those messages after the client “register “ to a CometContext //CometContex contains references to all suspended connections (encapsulated inside a CometHandler) 44

Step 2: Define a CometHandler • The CometHandler<E> interface has these methods //Invoked when CometContext.notify() is called public void onEvent(CometEvent ce); // Invoked when the browser close a suspended // connection or when the suspend timeout expire public void onInterrupt(CometEvent ce); // Invoked when the request is suspended public void onInitialize(CometEvent ce); // Attach an object // most probably the HttpServletResponse public void attach(E e); • Long Polling, in onEvent(event), > event.getCometContext().resumeCometHandler(this); 45

CometHandler: TTTHandler //Inside the TTTComet Servlet class... private class TTTHandler implements CometHandler<HttpServletResponse> { private HttpServletResponse response; //When a push operation happens, onEvent invoked after CometContext.notify() is called public void onEvent(CometEvent event) throws IOException { ... } 46

Step 3: Connect Comet Servlet: Add CometHandler to CometContext The Servlet Get (called by iframe) protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { TTTHandler handler = new TTTHandler(); handler.attach(response); CometEngine engine = CometEngine.getEngine(); CometContext context = engine.getCometContext(contextPath); context.addCometHandler(handler); } //The GET request is now suspended, awaiting further action before a response is returned //On first load, connects to server with a GET, not POST (Recommended by Comet) 47

Step 4: Advertise Changes Post is called (client) <table> <tr> <td id="cell0"><img id="img0" src="resources/0.gif" onclick=postMe("0")></td> ... </table> var url = "TTTComet1"; function postMe(arg) { ... var xhReq = new createXMLHttpRequest(); xhReq.open("POST", url, true); xhReq.setRequestHeader("Content-Type", "application/x-www-form-urlencoded"); xhReq.send("cell="+arg); }; 48

Step 4: Advertise Changes Post is called (server) protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String cellStr = request.getParameter("cell"); PrintWriter writer = response.getWriter(); ...... game.turn(cell); ...... CometEngine engine = CometEngine.getEngine(); CometContext<?> context = engine.getCometContext(contextPath); context.notify(null); //attachment for CometEvent 49

Step 4: Advertise Changes • POST is called via a click on one client • We get the context again, and call context.notify() on server • This sends a NOTIFY event to the handler • The handler will now update all listening clients > Invode onEvent implemented in CometHandler > Sends a script which includes JSON formatted data > Closes all open connections when done 50

CometHandler: TTTHandler (revisit) //Inside the TTTComet Servlet class... private class TTTHandler implements CometHandler<HttpServletResponse> { private HttpServletResponse response; //When a push operation happens, onEvent invoked after CometContext.notify() is called public void onEvent(CometEvent event) throws IOException { if (CometEvent.NOTIFY == event.getType()) { PrintWriter writer = response.getWriter(); writer.write( "<script type='text/javascript'>parent.chImg(" + game.getJSON() + ")</script>n"); writer.flush(); event.getCometContext().resumeCometHandler(this); } } 51

Step 5: Client Side update (called from Server Side onEvent() in CometHandler) function chImg(args) { var data = eval(args); // redraw the board for (i = 0; i < 9; i++) { document.getElementById("img"+i).src= "resources/"+data.board[i]+".gif"; } // -1 is unfinished, 0 is tie, 1 is X win, 2 is O win var statusMsg; if (data.win == 0) { statusMsg = "It's a tie!"; } else if (data.win == 1) { .... document.getElementById("gstatus").innerHTML = statusMsg; 52

Sample JSON output { “win”: “-1”, “board”: [“0”, “1”, “10”, “0”, “1”, “10”, “1”, “10, “0” ], “turn”: “10” } 53

Two Player Game: Tic Tac Toe Demo 54

What is Atmosphere Comet techniques aren't standardised among Web Container • Atmosphere is a POJO based framework using Inversion of Control (IoC) to bring Comet to the masses. • A Framework which can run on any Java based Web Server. > Automatically detects native Comet API and use it. > Fallback to one thread per connection in case no native Comet support (ex: Tomcat 4) • Run on top of Servlet 2.5 compliant Web Server • Support Servlet 3.0 Async API > Auto-Detect Servlet 3.0 API • Easily embeddable into other framework > Ex: Jersey, Grails, Scala, Struts, Cometd, etc. 56

Architecture Reuse experience and code...from Grizzly Comet to Jersey! Atmosphere Core Jersey Atmosphere plug in Atmosphere CPR Comet Portable Runtime Servlet 3.0 Grizzly Jetty JBoss WLS Blocking WS External Module Application API Atmosphere Module 57

Getting started with Atmosphere CPR • Three API to know > AtmosphereHandler: Your POJO representing your application. Quite simple: ● When a request comes in: onEvent(AtmosphereEvent) ● When a broadcast happens: onMesage(AtmosphereEvent) > Broadcaster: Share Data between suspended connection. > BroadcasterFilter: Manipulate broadcasted data before they get written 58 58

Example: AtmosphereHandler onEvent() public AtmosphereEvent onEvent( AtmosphereEvent<HttpServletRequest, HttpServletResponse> event) throws IOException { HttpServletRequest req = event.getRequest(); HttpServletResponse res = event.getResponse(); ... if (req.getMethod().equalsIgnoreCase("GET")) { ... res.getWriter().flush(); event.suspend(); } if (req.getMethod().equalsIgnoreCase("POST")) { synchronized (game) {... Broadcaster bc = event.getBroadcaster(); String response = game.getJSON(); // broadcast the updated game state bc.broadcast(response); writer.flush(); if (game.win() != -1) { game = new TTTGame(); } } } return event; } 59

Example: AtmosphereHandler onMessage() public AtmosphereEvent onMessage( AtmosphereEvent<HttpServletRequest, HttpServletResponse> event) throws IOException { // Client closed the connection. if (event.isCancelled()) { return event; } String response = (String) event.getMessage(); response = "<script type='text/javascript'>parent.chImg(" + response + ")</script>n"; PrintWriter writer = event.getResponse().getWriter(); writer.write(response); writer.flush(); if (!event.isResumedOnTimeout()) { event.resume(); } return event; } 60

Getting started with Atmosphere Core • All the power of REST and Jersey functionality, plus > @Suspend : suspend a response > @Resume: resume a response > @Broadcast: Broadcast events > @Cluster: Cluster your Broadcast > @BroadcasterFilter • Subset of Atmosphere CPR available via injection > AtmosphereEvent > Broadcaster 61 61

Example: Writing a REST application @Suspend // the returned String will be written and then response suspended @GET @Produces("text/html") public String cometGet() { return "n"; } @Broadcast // The returned String will be broadcasted to all suspended response. @Consumes("application/x-www-form-urlencoded") @POST @Produces("text/html") public String cometPost( @FormParam("action") String action, @FormParam("name") String name, MultivaluedMap form) { if ("login".equals(action)) { return BEGIN_SCRIPT_TAG + toJsonp("System Message", name + " has joined.") + END_SCRIPT_TAG; } else if ("post".equals(action)) { return BEGIN_SCRIPT_TAG + toJsonp(name, form.getFirst("message")) + END_SCRIPT_TAG; } else { throw new WebApplicationException(422); 62 } }

Atmosphere Plugs In: What is that? • Set of classes and annotation that bring new functionality > Clustering Atmosphere ● Using @terracotta, @Shoal, @JGroup > Container specific functionality ● Tomcat and Grizzly supports asynchronous I/O > Any community provided annotation/classes 63 63

Summary The Asynchronous Web Revolution is Now • The Asynchronous Web will revolutionize human interaction • Push can scale with Asynchronous Request Processing • Writing Games is not that complicated • With GlassFish project and Project Grizzly, the revolution begins with your application today! • Get ready for Atmosphere and Servlet 3.0 64

For More Information • Getting Started with GlassFish and Comet > http://weblogs.java.net/blog/jfarcand/archive/2008/04/the_hitchhikers .html > http://weblogs.java.net/blog/jfarcand/archive/2006/10/writting_a_come.ht > https://atmosphere.dev.java.net/ ● user@atmosphere.dev.java.net or dev@atmosphere.dev.java.net) • Grizzly Active’s Bloggers: > Alexey: http://blogs.sun.com/oleksiys/ > Shing Wai: http://blogs.sun.com/swchan/ > John: http://weblogs.java.net/blog/johnmann/ > Sebastien: http://www2.sebastiendionne.ca > Jeanfrancois: http://weblogs.java.net/jfarcand • Project Grizzly > http://grizzly.dev.java.net ● dev@grizzly.dev.java.net & users@dev.grizzly.java.net 65

Doris Chen Ph.D. doris.chen@sun.com Staff Engineer/Technology Evangelist 66

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Developing Revolutionary Web Applications using Comet and Ajax Push

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Developing Revolutionary Web Applications using Comet and Ajax Push — Presentation Transcript