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Extending the J2EE Deployment API for Disruption-Free Service

WebLogic Server goes above and beyond the specification

J2EE has been very successful in providing the specifications for detailing the arrangement of resources in a server-side application such as a:

  • Web application (*.war file)
  • EJB application (*.jar file)
  • Enterprise application (*.ear file)
This in itself has helped make J2EE popular in the enterprise. The next step is to ease the process of deploying applications across various environments by providing a uniform deployment API supported by different J2EE product vendors. Along with the deployment API, there needs to be a uniform management API supported by different J2EE product vendors to manage the deployed application in production.

It is common for a J2EE application server vendor to offer some deployment tools along with the application server distribution. In fact, administrators depend on the application deployment and application configuration tools they provide. Creating scripts or automating the deployment process involves implementing vendor-specific APIs. Standardizing this aspect will simplify the development of deployment and application configuration tools. There would only be one package to implement.

J2EE Deployment API
This specification defines standard APIs that enable any deployment tool that uses the Deployment API to deploy any assembled application onto a J2EE-compatible platform.

The API addresses the three-stage deployment process:

  • Installation: Moves the properly packaged components to the server
  • Configuration: The resolution of all external dependencies declared by the application
  • Undeployment: Removes the application from the server
The Need for Extensions
The J2EE Deployment API in its current 1.1 version as part of the J2EE 1.4 specification pretty much achieved this goal, but it can be enhanced in certain areas to provide more practical features. For example, the redeployment process isn't detailed and the maintenance of the HTTP session objects during application updates is omitted. Versioning of applications isn't part of the Deployment API either.

Live application upgrade is one of the main factors in achieving disruption-free service. Even though the failover feature provided by WebLogic Cluster will increase the availability of an application, a live application update is vital to providing continual uptime of the service to clients.

In this article we'll discuss some of the specification enhancements needed. To illustrate, we'll detail them on Diablo, the upcoming WebLogic Server 9.0.

WebLogic Server Extensions to the J2EE Deployment API
Exporting Application to Deploy Across Multiple Environments

One of the biggest challenges for an administrator of a J2EE deployment platform is to successfully transition the application from the development environment to the testing and production environments. Along with the application to be deployed developers need to transfer the knowledge about the application's dependent resources. It's always a challenge for application deployers and system administrators to resolve such dependencies for each application when transitioning the application from a development to a live environment.

The J2EE runtime environment or container provided by an application server vendor provides many infrastructure services to the application that can be configured with the deployment descriptors. J2EE also provides a way to abstract everything that is not constant in an application by configuring them in the deployment descriptors rather than hard coding them in the application. Changing the application deployment descriptors doesn't require any change in the application source.

Having accepted the premise that change is constant in this world, change in an application involves changing deployment descriptors, which involves unpacking the application archive and repackaging it. To take advantage of the vendor-specific application configuration options used for optimizing the performance of the application components in production, the vendor-specific deployment descriptors inside the archive should be modified such as, for example, EJB pool size.

Developers can use weblogic.Configure, a command-line tool provided by BEA, to export an application's configuration. Then they can select the WebLogic-specific deployment descriptor properties that have to change when the application is deployed in another environment such as EJB pool size, EJB cache size, etc. The tool will create a deployment plan with variable definitions for the descriptor properties selected. Later when the application is being deployed using any one of the WebLogic deployment tools, the plan variables are presented to a deployer for customization.

WebLogic-specific deployment descriptor properties are classified as:

  • Non-configurable: Properties that can't be changed by an administrator
  • Dependency: Properties that resolve to a resource configured in the target WebLogic domain (for example, the JDBC Data Source being used by an EJB)
  • Declaration: Properties to declare a resource that other applications will use (for example, the JNDI name of an EJB)
  • Configurable: Properties that aren't configured as Dependency or Declaration will be configurable (WebLogic-specific properties such as an EJB cache size fall into this category)
For an entire category for deployment descriptors a template deployment plan can be generated through the command-line tool weblogic. Configure.

java weblogic.Configure -root install_root
[-type (ear|war|jar|car|rar|jms|jdbc)]
[-export (all|dependencies|declarations|dynamics)]

More Stories By Balamurali Kothandaraman

Balamurali Kothandaraman is a delivery technologist for education services at BEA Systems Inc. He has over 7 years of experience in Java and J2EE technologies and is a BEA Certified Server Specialist, Administrator, and Instructor. Bala is a frequent speaker at various conferences, including eWorld and JavaOne.

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