J2EE APIs usually used in the middle tiers or between the tiers
- JDBC from App Server to Database Server
- JavaMail from App Server to Mail Server
- HTTP/SOAP between applications/architectures
- HTTP/S is used from the client to the Web Server (Servlets/JSPs)
- JMS/JTS used to communicate with other enterprise systems
The J2EE interoperability
(From Sun's J2EE specification v 1.4)


