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6.3.2: Setting properties for a module

6.3.2: Setting properties for a module

A module's properties are used to create a deployment descriptor for the module. The properties represent the deployment descriptor elements as defined in the J2EE specifications. The Application Assembly tool automatically creates deployment descriptor files based on values entered in the property dialog boxes and wizards. The deployment descriptor is an XML document that contains application configuration data that the run-time uses. In general, a deployment descriptor contains the following information:

  • Information about the content of the module being assembled. For example, for an EJB module, the deployment descriptor lists each enterprise bean's class, home interface class, remote interface class, whether the bean is an entity or session bean, and the bean's attributes (such as persistence management type and primary key class for entity beans).

  • References to a module's internal and external dependencies (such as enterprise beans, databases, and resource connection factories needed by the module). Internal dependencies are dependencies on other components within the same module. External dependencies are dependencies on components residing outside of the module. For example, an enterprise bean in an EJB module can require another enterprise bean that is not packaged in the same module. The deployment descriptor can contain references to the remote bean's home interface. The deployment descriptor can also include JNDI binding information that the container uses to locate the remote bean at install time.

  • Run-time-specific information needed by the application. For example, the servlet mappings needed for a Web application or the persistence management (BMP or CMP) to be used by an entity bean.

  • References to security roles. Security information is used when the module is deployed.

In addition to XML files, the Application Assembly Tool automatically generates XMI files to store binding and IBM extension information. Binding information maps a resource (enterprise bean or resource connection factory object) from the logical name specified in the deployment descriptor to its actual name in the global JNDI namespace. IBM deployment descriptor extensions are additions to the standard descriptors for J2EE applications, Web applications, and enterprise beans. The extensions allow you to specify properties that enable Enterprise Edition or legacy (older) systems to work in the WebSphere Application Server environment. For example, an extension property is used to define how to manage transaction scoping for an enterprise bean's methods.

A J2EE application contains one application-level deployment descriptor file, governing the application as a whole. It also contains a component-level deployment descriptor file, one governing each module in the application. For example, the application-level deployment descriptor specifies security information for the application and defines how often the application is to be reloaded. The component-level deployment descriptor (for example, for an EJB module) specifies the following:

  • General properties of the EJB module, such as the location of class files needed for a client program to access the enterprise beans in the module and the icons to be associated with the module.

  • The deployable enterprise beans that the module will contain.

  • Security roles used to access resources in the module.

  • Transaction attributes for the enterprise bean methods.

  • A default datasource to be used by entity beans in the module, if one is not specified.
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