Using the Java 2 Platform, Standard Edition (J2SE) as a basis, Java 2 Platform, Enterprise Edition (J2EE) builds on top of this to provide the types of services that are necessary to build large scale, distributed, component based, multi-tier applications. Essentially, J2EE is a collection of APIs that can be used to build such systems, although this is only half of the picture. J2EE is also a standard for building and deploying enterprise applications, held together by the specifications of the APIs that it defines and the services that J2EE provides. In other words, this means that the "write once, run anywhere" promises of Java apply for enterprise applications too:
- Enterprise applications can be run on different platforms supporting the Java 2 platform.
- Enterprise applications are portable between application servers supporting the J2EE specification.
The J2EE is a very comprehensive platform and at first the range of technologies and APIs can seem daunting. By building up your knowledge of J2EE piece by piece, technology by technology, you'll soon be a good position to start designing and building J2EE systems. Next month we'll start our tour of the various J2EE technologies by taking a closer look at the web tier (Java Servlets and JSP) including a discussion of how they fit in to the J2EE, how Java Servlets and JSP coexist and also the sort of things that they are both capable of.