de.cismet.ext

Interface CExtProvider<T>

public interface CExtProvider<T>

This interface can be used to provide extensions that can be loaded into applications that support the extension mechanism. It is the main extension point of cismet applications. Implementations shall be put on the global Lookup and will be collected on demand by the CExtManager. It is crucial that implementers take care about the ordering/positioning within the Lookup. Thus they shall make appropriate use of the ServiceProvider.position() property.

Version:

1.0, 2012/08/28

Author:

thorsten, mscholl

See Also:

Lookup, ServiceProvider

Method Summary

Modifier and Type	Method and Description
boolean	canProvide(Class<?> c) Shall return a boolean indicating whether this provider implementation provides extensions of this type.
Class<? extends T>	getType() Shall return a Class that indicates which kind of extensions this implementation of CExtProvider delivers.
Collection<? extends T>	provideExtensions(CExtContext context) Shall provide extensions for the given context.

Method Detail

provideExtensions

Collection<? extends T> provideExtensions(CExtContext context)

Shall provide extensions for the given context. Implementers are obliged to provide implementations of the requested extension in the correct order if they intend to provide more than one implementation. "Correct order" means that the implementations are ordered from most relevant to least relevant. E.g. an implementation of CExtProvider plans to provide two implementations of MyService, a default one (DefaultMyService) and a specific one for a special kind of context (SpecificMyService). If this CExtProvider is requested to provide extensions with the afore mentioned special kind of context, so that it matches the DefaultMyService and the SpecificMyService requirements, the returned collection shall have the order [SpecificMyService, DefaultMyService]. Additionally, if the extension provider will not provide any implementation for a certain context it shall return an empty collection. This implies that this operation shall never return null.

Parameters:

context - the context for which the extensions are requested, may be null

Returns:

a collection of extension implementations, never null

getType

Class<? extends T> getType()

Shall return a Class that indicates which kind of extensions this implementation of CExtProvider delivers.

Returns:

the type of the provided extensions, never null

canProvide

boolean canProvide(Class<?> c)

Shall return a boolean indicating whether this provider implementation provides extensions of this type. Basically this operation is closely related to getType() and may probably do something like c.isAssignableFrom(getType()). However, this operation can also be implemented in another way to avoid loading of the extension class if the return value of this operation will be false.

Parameters:

c - the type which is tested if instances of it can be produced by this provider implementation

Returns:

true if the provider provides instances of the given type, false otherwise