Can XMPP be used like Comet's http long wait?
Yes. Take a look at XMPP over BOSH. It's a long-lived non-polling technique. From the BOSH specification:
This specification defines a transport protocol that emulates the semantics of a long-lived, bidirectional TCP connection between two entities (such as a client and a server) by efficiently using multiple synchronous HTTP request/response pairs without requiring the use of frequent polling or chunked responses.
jbosh is an open source Java implementation. Tigase.org has a number of projects, including BOSH support, and appears to be mostly Java/GWT. JAXMPP is a Java library in the framework, although it's not clear what feature set it supports. I've not tried any of these myself.
- Like Ire told you can use bosh for that. On the client-side(javascript) you could use strophe.js.
- Prosody is an easy to install XMPP-server which supports BOSH.
- To learn how to create programs using strophe.js you could read Professional XMPP programming with javascript and Jquery