There are two types of deployment descriptors: J2EE and runtime. A J2EE deployment descriptor is defined by a J2EE specification and can be used to configure deployment settings on any J2EE-compliant implementation.
A runtime deployment descriptor is used to configure J2EE implementation-specific parameters. For example, the Sun
Java System Application Server Platform Edition 8 runtime deployment descriptor contains information such as the context root of a Web application, the mapping of portable names of an application's resources to the server's resources, and Application Server implementation-specific parameters, such as caching directives.
The Application Server runtime deployment descriptors are named sun-moduleType.xml and are located in the same directory as the J2EE deployment descriptor.
Reference Website http://java.sun.com/j2ee/1.4/docs/tutorial/doc/Overview5.html
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