As more and more application servers that comply with the new J2EE 1.4 spec become available, Java developers will have to consider how -- and if -- they should migrate their J2EE 1.3-compliant code. In this article, David Currie takes a look at the changes to one particular area of the J2EE specification: messaging. You'll see what you'll need to change, what you can leave as is, and what new opportunities await you.