JMS is a Java-based API that is like a GATEWAY to the MESSAGE-oriented middleware like SONICMQ, IBM MQSeries etc. It provides a mechanism for sending and receiving messages by making use of the publishing/subscribe (1 message multiple receivers) model or point-to-point (1 message 1 receiver) paradigm from one client to another. 

The following image describes how 2 clients can communicate with each other utilizing JMS providers.

J2EE DEFINES standards and specifications for various COMPONENTS such as e-mailing, database connectivity, security, XML parsing, CORBA communication etc that help in developing complex, reliable, secure and distributed servlets and applications that follow the client-server model. It provides various API interfaces that act as standards between different vendor adapters and J2EE components. This ensures that the application components are not dependent on vendor codes. Due to this, J2EE has been very popular among Java developers in the field of software development.