The Java EE 7 Tutorial
A Resource Adapter Archive (RAR) file stores XML files, Java classes, and other objects for Java EE Connector Architecture (JCA) applications. A resource adapter can be deployed on any Java EE server, much like a Java EE application. A RAR file can be contained in an Enterprise Archive (EAR) file, or it can exist as a separate file.
The RAR file contains
A JAR file with the implementation classes of the resource adapter
META-INF/directory that can store an
ra.xmlfile and/or an application server–specific deployment descriptor used for configuration purposes
A RAR file can be deployed on the application server as a standalone component or as part of a larger application. In both cases, the adapter is available to all applications using a lookup procedure.