A service provider interface (SPI) is the set of public interfaces and abstract classes that a service defines.
'Service Provider Interface: Creating Extensible Java Applications'. Services are units of sound-handling functionality that are automatically available when an application program makes use of an implementation of the Java Sound API In the Java Runtime Environment, SPIs are used in: The concept can be extended to other platforms using the corresponding tools. Providers can also be made available by adding them to the application's class path or by some other platform-specific means. Service providers can be installed in an implementation of the Java platform in the form of extensions, that is, jar files placed into any of the usual extension directories. The classes in a provider typically implement the interfaces and subclass the classes defined in the service itself. A service provider is a specific implementation of a service. A service is a well-known set of interfaces and (usually abstract) classes.
