Methods and software are described which provide the ability to use plug-ins to extend functionality for J2EE applications. The methods involve use of an application deployment package including a plug-in manifest file containing plug-in meta-data, a unique identifier for the plug-in and interconnection data representing interconnections to other plug-in packages. An extension registry service uses the plug-in package to provide extensibility to the application by locating plug-ins and determining the interconnections between them based on the interconnection data. The extension registry service collects plug-in packages dynamically as J2EE modules are loaded by the J2EE platform and maintains the unique identifiers for all extension point(s) and extension(s) defined in the plug-in packages. The extension registry is used to find the associated extensions when the application executes an extension point. Identified extensions can then be invoked by extension point code.