Java is divided (as far as i know) in tree, micro edition, standard edition, and enterprise edition. J2ee includes all the tecnology to build enterprise application frecuently applications that runs on servers. I hoope this help you.
Since Java 1.2, Sun started calling the technology as Java 2. So all the editions after that are called J2SE (standard), J2ME (micro) and J2EE (enterprise). JMS is a part of J2EE, that deals with asynchronous, guaranteed message delivery to "publishers" and "subscribers" applications or from one-app to another-app (point to point). It's similar in a way to Microsoft MSMQ, if you are aware of that.
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