Java 2 Platform, Enterprise Edition: Platform and Component Specifications

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Chapter J2EE.2: Platform Overview

This specification doesn't require that a J2EE product be implemented by a single program, a single server, or even a single machine. In general, this specification doesn't describe the partitioning of services or functions between machines, servers, processes, etc. As long as the requirements in this specification are met, J2EE product providers can partition the functionality however they see fit. A J2EE product must be able to deploy application components that execute with the semantics described by this specification.

A very simple J2EE product might be provided as a single Java virtual machine that supports applets, web components, and enterprise beans simultaneously in one container (although this would be an extreme, and probably rare, case), and application clients each in their own container. A typical low end J2EE product will support applets in one of the popular browsers, application clients each in their own Java virtual machine, and will provide a single server that supports both web components and enterprise beans. A high end J2EE product might split the server components into multiple servers, each of which can be distributed and load-balanced across a collection of machines. This specification does not prescribe or preclude any of these configurations.

In addition, this specification does not describe which of the components that make up a J2EE product must be packaged together in a single product. A vendor of a fully integrated J2EE product might provide a complete package that includes all the software required to provide the J2EE services as well as the underlyingoperating system and even hardware. A more typical J2EE product provider might provide a middleware application server along with components that allow the server to integrate with products from other vendors (e.g., a database, a web server) to provide the complete J2EE product. Some vendors may require that the end customer purchase and integrate significant additional components to create a J2EE product. This specification does not prescribe or preclude any of these approaches. In all cases, it is the responsibility of the J2EE product provider to describe to the customer exactly what to do to create an environment that is J2EEcompatible.

A wide variety of J2EE product configurations and implementations, all of which meet the requirements of this specification, are possible. A portable J2EE application will function correctly when successfully deployed in any of these products.

J2EE.2.3 Product Extensions

This specification describes a minimum set of facilities that all J2EE products must provide. Most J2EE products will provide facilities beyond the minimum required by this specification. This specification includes only a few limits to the ability of a product to provide extensions. In particular, it includes the same restrictions as J2SE on extensions to Java APIs. A J2EE product may not add classes to the Java programming language packages included in this specification, and may not add methods or otherwise alter the signatures of the specified classes.

However, many other extensions are possible. A J2EE product may provide additional Java APIs, either other Java standard extensions or other (appropriately named) packages. A J2EE product may include support for additional protocols or services not specified here. A J2EE product may support applications written in other languages, or may support connectivity to other platforms or applications.

Of course, portable applications will not make use of any platform extensions. Applications that do make use of facilities not required by this specification will be less portable. Depending on the facility used, the loss of portability may be minor or it may be significant. The Java 2 Platform, Enterprise Edition Application Programming Model 1 will help application developers construct portable applications, and will contain advice on how best to manage the use of non-portable code when the use of such facilities is necessary.

In addition, we expect J2EE products to vary widely, and in fact compete, on various quality of service aspects. Different products will provide different levels of performance, scalability, robustness, availability, security, etc. In some cases this specification describes minimum required levels of service. Future versions of this specification may allow applications to describe their requirements in these areas.

J2EE.2.4 Platform Roles

This section describes typical Java 2 Platform, Enterprise Edition roles. Although these roles are considered to be typical, an organization could use slightly different roles to match that organization's actual application development and deployment workflow.

The following sections describe the roles in greater detail. Subsets of some of these roles are defined in the EJB, JSP, and servlet specifications.

J2EE.2.4.1 J2 EE Product Provider

A J2EE product provider, typically an operating system vendor, database system vendor, appl server vendor, or a web server vendor, implements a J2EE product providing the component containers, J2EE platform APIs, and other features defined in this specification. A J2EE product provider must provide the J2EE APIs to the application components through the containers. A product provider frequently bases an implementation on an existing infrastructure.

A J2EE product provider must provide the mapping of the application components to the network protocols as specified by this specification. A J2EE product is free to implement the interfaces that are not specified by this specification in an implementation-specific way.

A J2EE product provider must provide application deployment and management tools...

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