The J2EE 1.3 specification (See Resources) defines a standard mechanism for hosting J2EE applications, which is known as the J2EE platform. The platform uses a component based approach to provide a multitiered, distributed, transactional model for enterprise applications. If that sounds like a mouthful, it certainly is. An application server that is compliant with the J2EE specification must provide services and APIs for:

• Enterprise JavaBeans Technology 2.0
• JDBC API 2.0
• Java Servlet Technology 2.3
• JavaServer Pages Technology 1.2
• Java Message Service 1.0
• Java Naming and Directory Interface 1.2
• Java Transaction API 1.0
• Java Mail API 1.2
• JavaBeans Activation Framework 1.0
• Java API for XML Processing 1.1
• J2EE Connector Architecture 1.0
• Java Authentication and Authorization Service 1.0

     As we will see, in order to manage this massive amount of functionality in a multitier, multithreaded, multiuser environment, the J2EE platform imposes a variety of restrictions on the development process, especially with regard to Enterprise JavaBeans.