...

• A bind method called when a service appears
• An unbind method called when a service disappears
  Moreover, callbacks can be in the component super class (in this case methods must be public).
  These methods can have

...

• four signatures:
• Without any argument: the method is just a notification
• With an object of the required service object : the object is the implicated service object
• With an OSGi service reference: the service reference appearing or disappearing
• With the service object and the OSGi service reference

The following component shows an example of implementation using this mechanism:

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• Dynamic policy (default) : the binding are managed dynamically. At each injection, the same provider is injected if the provider is always available. Else a new one is chosen. For aggregate dependency, the array order does not change, new providers are placed at the end of the array.
• Static policy : the binding is static. So, once bound a provider cannot disappear. If it disappears, the instance is invalidated and cannot be revalidated without stopping and restarting the instance.
• Dynamic-priority policy : the binding is managed dynamically but the injected provider is selected by using the OSGi ranking policy. Two injections can return two different providers, is a new provider is 'better' than the previous one, despite the first one is alway available. For aggregate dependency, the array is sorted.

A static binding is declared as following :

<component classname="...HelloConsumer">
<requires field="m_hellos" policy="static"/>
...
</component>

A dynamic-priority binding is declared as following :

<component classname="...HelloConsumer">
<requires field="m_hellos" policy="dynamic-priority"/>
...
</component>

Requires Metadata

A requires element metadata can contains :

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