7.6 Summary

The J2EE platform provides facilities to simplify the deployment process. It uses JAR files as the standard package for components and applications, and XML-based deployment descriptors for platform configuration and component customization. Tools that read and write application deployment descriptors also simplify deployment, because they present users with an intuitive view of application structure and component capabilities.

The J2EE packaging and deployment process involves three J2EE roles: application component provider, application assembler, and deployer.

Application component providers create components, package them into modules, and write their deployment descriptors. They design components with business logic that is customizable via deployment descriptors, instead of by modifications to the source code. When packaging components into modules, application component providers need to balance between the competing goals of reusability and simplicity.

Application assemblers resolve dependencies between deployment descriptor elements in different modules and assemble modules into larger deployment units. Deployers customize deployment descriptor elements for the application's deployment environment and install deployment units. The deployer must ensure that the values of all environment entries declared by an enterprise bean are meaningful.

The packaging and deployment process is handled best by specialized tools. While both component providers and deployers need to deploy applications, their deployment needs are different. Component providers want fast response times, and the ability to undeploy, redeploy, and partially deploy applications easily and quickly. Deployers in a production environment require robustness, performance, and stability. Deployment tools need to address both sets of requirements while supporting such J2EE platform goals as portability and backwards compatibility.