I have solved my problem ... but I don't understand why it makes such a difference between 3.0 and 2.4.4!
In fact, due to a bug in our application, it tried to open a very large quantity of files that do not exist (hundreds!).It does that with "this.getClass().getResourceAsStream(fileName)".
Correcting this bug solves the bad answer time with JBoss 3.0.But I still can't figure out why this bug had not the same effect on the performance with JBoss 2.4.4! I use the same JDK running on the same hardware/os....
might be an issue of unified loader repository searching thru many classloaders before finding your resource.. (or in this case realizing they don't exist at all).