J2EE Platform Roles
To create, package, and deploy any J2EE application—other than the simplest—requires the effort of more than one person or organization. For example, in the development arena, a team of developers will write the J2EE components and someone else will assemble the finished application. In the production environment, someone will configure the J2EE environment and deploy the application, and yet another person will monitor the running application and its physical environment. In smaller organizations, there may be no physical distinction between these roles, but they will still be logically separate.
This team, together with Product Providers and Tool Providers, constitute the J2EE platform roles. It is these roles that this section explores.
J2EE Product Provider
A J2EE product must include the component containers and J2EE APIs that conform to the J2EE specification; today's lesson has introduced all of these containers and APIs. Examples of J2EE products include operating systems, database systems, application servers, and Web servers. An organization that supplies a J2EE product is known as the J2EE Product Provider.
The J2EE Product Provider is also responsible for mapping application components to defined network protocols. In addition, the Product Provider must provide deployment tools for the Deployer and management tools for the System Administrator.
The Product Provider is free to provide implementation-specific interfaces that the J2EE specification does not define. Hence, you will occasionally see a warning in a lesson that highlights a vendor-specific piece of functionality.
A list of J2EE compliant vendor offerings is available from http://java.sun.com/j2ee/compatibility.html.
Application Component Provider
As you have already seen, a J2EE application consists of components, but it also may consist of other resources, such as HTML pages or XML files. The Application Component Provider creates both these resources and components. Almost all organizations will use several component providers. They may exist in-house, or the organization may outsource component creation or buy in components. Whichever is the case, specialists in the different tiers (presentation, business, and data access) will write the components that relate to that tier. For example, a business tier specialist will write EJBs, whereas a presentation tier expert may write JSPs.
Application Assembler
The Application Assembler's job is to package the application, written by the Application Component Providers, into a J2EE application. The application is packaged into an Enterprise Application Resource (EAR) file (also known as an Enterprise Archive) that must conform to the J2EE specification. Apart from this assembly, the Application Assembler is responsible for providing instructions that state the external dependencies of the application.
Application Deployer
The Application Deployer role is the first that requires knowledge of the production environment. This is because the Application Deployer must deploy the application into that environment. Specifically, the Application Deployer must install, configure, and start the execution of the application.
The installation process is where the Application Deployer moves the application to the server and installs any classes the container requires to perform its duties. During the configuration process, the Application Deployer satisfies any external dependencies that the Application Assembler has stipulated and configures any local security settings (for example, modifies a policy file). The final stage, starting execution, is where the Application Deployer starts the application in readiness to service clients.
Systems Administrator
The Systems Administrator configures and maintains the enterprise network, and monitors and maintains the application once deployed.
Figure 2.4 shows the interactions between each of these roles and their interactions with the J2EE application.
Figure 2.4. J2EE roles.
Tool Provider
There are many tools to assist with the creation, packaging, deployment, and maintenance of J2EE applications. Currently, the J2EE specification only defines that the Product Provider must supply deployment and maintenance tools; it does not stipulate what these tools should be. Future releases of the specification are likely to provide further guidelines, so that Tool Providers can supply platform-independent standardized tools sets.