A stub is a directory that contains WebSphere® Application Server JAR files for compile-time support, WebSphere Application Server configurations for remote deployment and the corresponding Java™ developer kit (JDK). These stub directories allow you to build applications for a server when the corresponding runtime environment or test environment is not installed locally.
When you install the product package by using IBM® Installation Manager, you can optionally install stub directories available for every supported version of the WebSphere Application Server (stub directories are also available for WebSphere Portal Server). From the features list of the Installation Manager, the option to install stub directories are labelled: Tools for developing applications without a local server installation
The default installation setting of a stub directory for WebSphere Application Server is x:\runtimes\base_v#_stub, where x is the installation directory where this product is installed and # is the version-level of the server. For example on a Windows operating system, the default installation setting of the WebSphere Application Server V8.0 stub directory is: C:\Program Files\IBM\SDP\runtimes\base_v8_stub