When you say hot deployment, did you mean dynamic deployment which does not require server restart? If yes, all the current deployment mechanisms in glassfish are dynamic which do not require server restart.
And directory deployment, which does not require re-packaging the application after making changes, is very convenient for developers to use.
Here is a link to the documentation which talks about various deployment mechanisms:
http://docs.sun.com/app/docs/doc/820-4502/beadw?a=view
[Message sent by forum member 'hzhang_jn' (hzhang_jn)]
http://forums.java.net/jive/thread.jspa?messageID=333905