What is Cometd ? Why it is used and how to work on that

Question

i'm just a beginner in cometd , and i'm interested and wanted to learn what cometd is and what for it is used i googled it out and found some resource.Under the following link 1.http://docs.cometd.org/reference/installation.html#d0e346.

I tried out with the given demo but i could not able to get the expected output from it. can anybody post some resource url's so that i can learn ?

Morse

Answer 1

Disclaimer: I'm the CometD project leader.

CometD is a set of library to write web applications that perform messaging over the web.

Whenever you need to write applications where clients need to react to server-side events, then CometD is a very good choice. Think chat applications, online games, monitoring consoles, collaboration tools, stock trading, etc. See more at the preface.

CometD ships a JavaScript client library, a Java client library and a Java server library. This allows you to write applications in the browser with fine-grained logic and control on the server. The server library, being in Java, leverages the high scalability of the JVM and the powerful asynchronous I/O API that the JVM and the Servlet specification provide.

CometD is transport agnostic: you write your applications using high level APIs, and CometD takes care of delivering the messages over the wire using the best transport available: WebSocket or HTTP, also providing a transparent fallback in case WebSocket does not work.

CometD provides a clustering solution called Oort that allows you to scale horizontally your web applications.

CometD comes with a ton of features and an extended documentation along with tutorials and demos you can use as a starting point for your project.

Join CometD to start hacking on your CometD-based web applications.

The CometD tutorials are currently written for CometD 2.x, but a port to CometD 3.x (the current version of CometD) is currently underway, so that requires a bit of patience. But you can start right away by following the primer and deploying the demos.

I hope you can get started with CometD with the above references. Drop an email on the mailing lists for any help you may need.

Fable

You say that CometD is transport agnostic - that it will try to use websockets and if websockets are not available on the client, then it will fallback to http. But will it fall back to http streaming or http long polling? Comet has both of those implementations and I would like to know which one CometD (Comet+Bayeux) uses. – Flanders

CometD uses HTTP long-polling. HTTP streaming has proven to be difficult to implement properly in case of transparent proxies that buffer or cache content. – Fable