Getting subject from Ejb container?

[belal]

Hi,

I found there are 2 ways to get the subject from the ejb container,

1) InitialContext ic = new InitialContext();
Subject subject = (Subject)ic.lookup("java:comp/env/security/subject");

2) AccessControlContext ctx = AccessController.getContext();
Subject subject = Subject.getSubject(ctx);

first option works successfully, but the second option fails (subject is null)!!

which one is JAAS/J2EE standard? why the second one didn't work? and when and why to use either option?

thanks,
Belal