The Avalon Repository SPI extends the API to provide a set of services that define the contact for plugin facilities. The Avalon Repository main bootstrapping system provides out-of-the-box support for concurrent deployment of multiple repository implementations enabling complete customization and future-proof evolution of artifact access and deployment needs. It achives this functionality by applying the same plugin process to its own implementation.

A plugin facility is requred to impliment one of the following ranked constructor patterns.

public MyFactory( 
    InitialContext context, 
    ClassLoader classloader )
{
}

public MyFactory( 
    InitialContext context )
{
}

public MyFactory( 
    ClassLoader classloader )
{
}

public MyFactory()
{
}

The object established by the factory constructor must implement the Factory interface.

public interface Factory
{
   /**
    * Return a new instance of default criteria for the factory.
    * @return a new criteria instance
    */
    Map createDefaultCriteria();

   /**
    * Create a new instance of an application.
    * @return the application instance
    */
    Object create() throws Exception;

   /**
    * Create a new instance of an application.
    * @param criteria the creation criteria
    * @return the application instance
    */
    Object create( Map criteria ) throws Exception;

}

A client on aquiring the factory will get the default criteria value and use this to parameterize the factory. On completion of parameterization (by setting application specific named values), the create operation is invoked and returns a new instance of the facility.