All HTTP responses require the client to initiate them, even those made using AJAX. But GMail's chat feature is able to receive messages from other users, even when I'm just sitting in my comfy computer chair watching but not interacting with the browser. How did they do it?
推荐答案
这种技术被称为彗星"，也被称为服务器推送"、反向ajax"等.
That tech is known as "comet", but also as "server push", "reverse ajax", etc.
It's about pushing data from the server to the browser, keeping an http connection alive. Find more info on it on the wikipedia article (English version).
这里还有一个 相当不错的演示文稿，来自 DWR 的 Joe Walker，他在哪里谈论彗星.
Also here's a pretty good presentation with Joe Walker from DWR, where he talks about comet.
