J2EE covers a lot of ground. The EJB spec instructs us not to mess about with our own Threads, but most containers have some non-standard way to spin off other threads. Asynchronous messaging is one standard way that doesn't give you a lot of control like waiting or joining the other
thread.
I'm really not sure about the
servlet container ... I've done a very limited bit of thread management in code called by servlets. Review the spec before going that route.
What kind of problem are you trying to solve?