Cometd with Jetty
A scalable Ajax/Coment framework
Cometd is a scalable HTTP-based event routing bus that uses a push technology pattern known as Comet. The term 'Comet' was coined by Alex Russell in his post 'Comet: Low Latency Data for the Browser'. Cometd consists of a protocol spec called Bayeux, javacript libraries (dojo toolkit), and an event server.
Jetty now has just an implementation of the cometd event server that uses the Continuation mechanism for asynchronous servlets.
Jetty already has comet implementations for DWR and activemq, but both of these use custom protocols which can lead to interoperability problems that cometd intends to solve.
Because browsers commonly permit only two connections to each server, it is not possible for a web page to use more than one Ajax library that is using comet techniques. The intent of cometd is to define a common protocol that can be shared between libraries and thus encourage interoperability.
Cometd provides a two multi-channel communications paradigm that allows asynchronous message delivery from server to client as well as client to server. The multi-channel nature of the protocol, will eventually allow a single comet connections to be shared between multiple Ajax toolkits
Jetty has implemented the server side of this protocol, which will allow it to be used with whatever client side implementations emerge (currently only dojo, but I plan to port activemq once it is stable). However to achieve true interoperability, we will need to develop standardized APIs on both the client and server side. Having standard protocol is a start on this, as it defines the capabilities that will need to be expressed in the APIs
Re: Cometd with Jetty
Re: Cometd with Jetty
We are using cometd on a project at my company and have run into an issue that we could really use some help with.
We are using JBoss with Tomcat 5.5 and I was hoping to keep things that way, so I put the cometd and jetty jar files into my webapp. What appears to be happening is that when two or more clients are connected through the cometd servlet (using dojo.io library), only the last client within the subscribers list will actually have a message delivered to them. After some debugging, it looks like only that last client actually has a Continuation. Is this possibly a by-product of using Tomcat instead of Jetty, or do you think there might be something else going on?