ibm-ejb-jar-ext.xmi 的作用

西湖鱼

　　用RAD开发EJB差不多一年多的时间了，但是对于RAD部署EJB的几个descriptor文件还是不甚了解，特别是ibm-ejb-jar-ext.xmi的作用，因为平时根本不会用到这个文件，被一个妹子问起这个文件的作用，一时竟然答不出来，好囧！
　　今天特别地搜了一下，才发现，好像也真没多大作用，但起码是一种了解，写在这里一下，提醒自己。
　　
Deployment descriptors
A deployment descriptor contains configuration data that the runtime environment uses for an application. A deployment descriptor can include information about the following:

The structure and content (enterprise beans, for example) of the application.
References to internal and external dependencies.
　　For example, an enterprise bean in an EJB module can require another enterprise bean that is not bundled in the same module.
References to resource factory objects, such as URLs or JDBC data sources.
Security roles that the container uses when implementing the required access control for the application.
Transactional information about how (and whether) the container is to manage transactions for the
　　application.
　　Deployment descriptors are XML files packaged with the application's files in a Java archive file. An EJB deployment descriptor is called ejb-jar.xml and is located in the META-INF folder of an EJB project. A J2EE application contains one application-level deployment descriptor file, governing the application as a whole. It also contains several component-level deployment descriptors, one for each module in the application.

In addition to standard deployment descriptors, the workbench also includes information on WebSphere Application Server bindings and extensions. The bindings and extensions documents are specific to IBM. Both binding and extension descriptors are stored in XMI files, ibm-ejb-jar-bnd.xmi and ibm-ejb-jar-ext.xmi, respectively.
　　Binding information maps a logical name of an external dependency or resource to an actual JNDI name. For example, the container uses binding information to locate a remote bean at installation.
　　Extensions are additions to the standard descriptors. The extensions enable older (legacy) systems to work in the WebSphere Application Server environment. They are also used to specify application behavior that is vendor-specific, undefined in a current specification, or expected to be included in a future specification.