J2EE.8.1 Application Development Life Cycle

The development life cycle of a J2EE application begins with the creation of discrete J2EE components. These components are then packaged with a component level deployment descriptor to create a J2EE module. J2EE modules can be deployed as stand-alone units or can be assembled with a J2EE application deployment descriptor and deployed as a J2EE application.

Figure J2EE.8-2 shows the life cycle of a J2EE application.

Figure J2EE.8-2. J2EE Application Life Cycle

J2EE.8.1.1 Component Creation

The EJB, Servlet, and application client specifications include the XML document type definition (DTD) of the associated component level deployment descriptors and component packaging architecture required to produce J2EE modules. (The application client specification is found in Chapter J2EE.9 of this document.)

J2EE.8.1.2 Component Packaging: Composing a J2EE Module

A J2EE module is a collection of one or more J2EE components of the same container type with one component deployment descriptor of that type. Deployment descriptors for J2EE modules are extensible. Any number of components of the same container type can be packaged together with a single container-specific J2EE deployment descriptor to produce a J2EE module.

• A J2EE module represents the basic unit of composition of a J2EE application.

• The deployment descriptor for a J2EE module contains all of the declarative data required to deploy the components in the module. The deployment descriptor for a J2EE module also contains assembly instructions that describe how the components are composed into an application.

• An individual J2EE module can be deployed as a stand-alone J2EE module without an application level deployment descriptor.

• The J2EE platform supports the use of bundled extensions as specified in Support for Extensions and Applications in Version 1.2 of the Java Platform (available at http://java.sun.com/products/jdk/1.2/docs/guide/extensions/spec.html).

J2EE.8.1.3 Application Assembly

A J2EE application consists of one or more J2EE modules and one J2EE application deployment descriptor. A J2EE application is packaged using the Java archive (JAR) file format into a file with a .ear (enterprise archive) filename extension. A minimal J2EE application package will contain only J2EE modules and the application deployment descriptor. A J2EE application package may also include libraries referenced by J2EE modules, help files, and documentation to aid the deployer, etc.

The deployment of a portable J2EE application should not depend on any entities that may be contained in the package other than those defined by this specification. Deployment of a portable J2EE application must be possible using only the application deployment descriptor and the J2EE modules (and their dependent libraries) and descriptors listed in it.

The J2EE application deployment descriptor represents the top level view of a J2EE application's contents. The J2EE application deployment descriptor is specified by the J2EE: application XML document type definition (DTD) (see Section J2EE.8.4, "J2EE:application XML DTD").

J2EE.8.1.3.1 Customization

In certain cases, a J2EE application will need customization before it can be deployed into the enterprise. New J2EE modules may be added to the application. Existing modules may be removed from the application. Some J2EE modules may need custom content created, changed, or replaced . For example, an application consumer may need to use an html editor to add company graphics to a template login page that was provided with a J2EE web application.

J2EE.8.1.4 Deployment

During the deployment phase of an application's life cycle, the application is installed on the J2EE platform and then is configured and integrated into the existing infrastructure. Each J2EE module listed in the application deployment descriptor must be deployed according to the requirements of the specification for the respective J2EE module type. Each module listed must be installed in the appropriate container type and the environment properties of each module must be set appropriately in the target container to reflect the values declared by the deployment descriptor element for each component.