CometD 介绍
CometD 是一个使用了 Ajax 推技术的可伸缩的基于HTTP的事件路由总线程序，这项技术也叫 Comet。
CometD is a Dojo Foundation project to
provide implementations of the Bayeux
protocol in javascript, java,
perl, python and other languages. Other organizations (eg. Sun, IBM and BEA)
also have implementations of Bayeux that are not strictly part of the CometD
project, but where possible they are linked to from this site.