Comet uses either Streaming or Long Polling to Push Events from the server to the client through a protocol like Bayeux. Carol's A Comet Slideshow Example... shows, through instructions, screenshots and samples, how to do this using dojo on the client (JavaScript) and Grizzly on the Server on the GlassFish Server. Check it out!

You may or may not know that Comet, Reverse Ajax, and Ajax Push are all synonyms and define a way to notify clients from a server. Jean-François has written many fine Comet blog entries, but this GlassFish v3 documentation on Comet is a very well written intro to the Comet paradigm and how to use it inside GlassFish v3 based on the Hidden example. You may also hear from Jean-François on Comet in a recent interview from this past JavaOne as well as read Ted Goddard's slide deck on IceFaces and Grizzly Comet from last week's GlassFish Day at Jazoon.

The documentation also discusses the pros and cons of HTTP Streaming vs. Long Polling and explains how to code both.

Bindows was one of the first AJAX toolkits and they have just announced Comet support on their BindowsFaces product, a JSF library. Comet is supported through an adaptor interface and Bindows includes one standard adaptor - that for GlassFish Server. See Bindows Blog Entry and Comet Daily for the announcement. For more on BindowsFaces check the How to Use and Documentation Pages. Bindow's parent company, MB Technologies, recently joined the Sun Partner Program for GlassFish and should be in our Partner Showcase very soon.

I was going to wait until late next week, but I see that JFA's interview at InfoQ is out and the website is visible so no reason to wait. JFA's "free time" left by Alexey's lead role on Grizzly 2.0 is going to be reinvested into a Atmosphere a new project in the GlassFish Community that will focus on Comet. The project is just starting; the InfoQ article seems roughly accurate although some goal fine-tuning is still happening. I expect JFA will provide a more detailed description in a future blog entry.

Grizzly 1.8.0 is out and this one has a lot of new material, including GWT support, better OSGi Compliance, improved Comet Support, improved performance, SPI cleanup and many more (see JFA's note). Grizzly 1.8.0 has already been pushed into the latest GFv3 builds. Also see the Release Thread and the complete ChangeLog. Congrats to JFA, Oleksiy, and the rest of the team and community.

The latest episode (#12) of the GlassFish Podcast is out. This is an interview from last week with Jean-François "Grizzly" Arcand on Comet (aka AjaxPush).

This 20-minute podcast gets into the Comet paradigm, its availability in GlassFish v2 and v3, standardization in the forthcoming Servlet 3.0 specification, and more.

Note also that Jean-François will be delivering three presentations in Canada later this June (2008): Vancouver, Montreal, Toronto.

Shin Wai Chan has a nice set of blog entries ([1], [2]) on Comet (aka AJAX Push). He goes on to describe the code on both the client and the server and provides a link to a ready-to-use archive. The second part refines the introduction by describing the use of HTTP streaming. Although they are documented with an earlier version of GlassFish v3, they apply equally to the latest TP2 promoted build provided you start GlassFish with this http-listener property in domain.xml:      <property name="cometSupport" value="true"/>

Comet is not Ajax, it's not polling, and it's not traditional servlet either. This set of short articles is a good way to grasp the Comet paradigm.

Update: Jim has a refined version of Shin's example.

Jean Francois (Mr Grizzly) has been working on Comet for quite a while, and it is good to see his perseverance rewarded. GlassFish v2 has Comet support and, although the API will not be standarized until Servlet 3.0, you can use it today. JFA's Latest Writeup explains how to enable Comet, and provides pointers to several sample applications including a jMaki example, a chat program, ICEfaces and DWR examples. BTW, I don't remember if I metioned that we started an Engineering Services. Comet seems a good match for that, so if you are interested, drop an email to JFA. And stay tuned for more articles.

Jean-François "Grizzly" Arcand has posted two slide decks he used last month during his European tour : • Grizzly (covers basics, use in GlassFish V3, and the recent 1.7 release) • Comet, aka Ajax Push (if you ask Jean-François, it's the best thing since slided bread, and who knows, he may be right :)

Interesting Comet use-cases seem to be popping up on a regular basis. This time around IceFaces' Ted is showcasing the WebMC sample application to host a slide presentation over the internet. You can host your own infrastructure (maybe a great new feature for java.net) and check a demonstration here.

In the latest version of this fully-documented-but-not-yet-final software, the interesting part is the use of Grizzly Comet to scale to a very large number of connections without killing the server with threads (ARP at work here). Unfortunately, I don't believe Skype scales as well in the number of simultaneous connections. Does anyone have a suggestion for an alternate solution for a one-to-many broadcast? A streaming solution maybe...

Get the previous ICEfaces coverage here: [1], [2]

Grizzly has been updated to the latest Bayeux Spec. This includes all the distributions including Grizzly 1.0.19, GlassFish v2.1 (9.1ur1 b09), Sailfin and Grizzly snapshots/1.6.2. GlassFish v3 will follow soon. For more details, check out JFA's note.

Jean-Francois has put a lot of work into making Grizzly (and, by extension, GlassFish) fully capable of servicing Comet applications. He has also worked on documentation, providing an example of the server-side code for a Comet-enabled application in his blog. It's great stuff, but left readers with one obvious question: what about the client side? Well, now Jean-Francois has that one covered too. In his latest blog entry, he shows how to write the client portion of a Comet app. His example uses the Prototype and Behaviour JavaScript libraries, and--of course--it runs on GlassFish.

Comet (also known as "Long Lived HTTP Connections" or "Ajax Push") lets server-side applications notify changes to its clients (Server-Initiated Message Delivery). Typical use-cases include chat, document-sharing application or much more ambitious architectures. Bayeux is a JSON-based protocol specification of Comet and gCometd is the name of the implementation inside Grizzly 1.0.11+ (DOJO or Ajax only) and GlassFish v2 b35+ (JSP, JSF, servlet).

The Comet/Bayeux spec (0.1draft5) released by the Dojo foundation couple of months ago is now supported in GlassFish v2 build 52. Unfortunately, this specification breaks most comet clients. Jean-François "Grizzly" Arcand recommends that you update to the new DOJO library if that's what you're using (and you probably should be since writing a Bayeux client isn't trivial).

More generally on Comet, check out:

• Comet Basics
• A good presentation
• Writing a Comet web application using GlassFish
• This simple, yet very cool demo.

Jonas Jacobi and John Fallows have a good article on the JDJ describing the value of Cometd, Bayeux, et al. to implement Server-Initiated Message Delivery. The article refers to Jetty and Grizzly. It is very nice to see the increased adoption of these technologies, in some cases in real production - stay tuned for some forthcoming Adoption Stories. Check out the article and enjoy!

The Bayeux Tapestry is a famous depiction of the Battle of Hastings. The tapestry is also famous because it shows Halley's Comet so it is fitting that the name for the protocol proposed for Comet (see Ajaxian or TheAquarium) is Bayeux.

Bayeux is JSON based and allows a COMET client to interact with a server. CometD is an implementation but the protocol should enable others, and JeanFrancois and TAKAI have collaborated to do exactly that using Grizzly. This gCometd can be used in GlassFish expect it in a future build of GlassFish v2. For all all the details check JeanFrancois' blog, but stay tuned for more samples and improvements, specially now that TAKAI has been voted a Grizzly committer.

BTW, I don't want to brag, but check the picture in our intro from last October! :-)