Package org.apache.sling.commons.osgi

Class RankedServices<T>

java.lang.Object
org.apache.sling.commons.osgi.RankedServices<T>
Type Parameters:
T - Service type
All Implemented Interfaces:
Iterable<T>
@ProviderType public final class RankedServices<T> extends Object implements Iterable<T>
Helper class that collects all services registered via OSGi bind/unbind methods. The services are ordered by service ranking and can be iterated directly using this object instance. Implementation is thread-safe.

With Declarative Services 1.3 supporting field injection with multiple cardinality (leveraging Collections), this class should only be used if DS 1.3 cannot be used for some reason. DS 1.3 is using the same ordering as ServiceReference.compareTo(Object).

Usage example:

1. Define a dynamic reference with cardinality OPTIONAL_MULTIPLE in your service: 

 @Reference(name = "myService", referenceInterface = MyService.class,
     cardinality = ReferenceCardinality.OPTIONAL_MULTIPLE, policy = ReferencePolicy.DYNAMIC)
 private final RankedServices<MyService> myServices = new RankedServices<MyService>(Order.DESCENDING);

2. Define bind/unbind methods that delegate to the RankedServices instance:

 void bindMyService(MyService service, Map<String, Object> props) {
   myServices.bind(service, props);
 }
 void unbindMyService(MyService service, Map<String, Object> props) {
   myServices.unbind(service, props);
 }

To access the list of referenced services you can access them in a thread-safe manner:

 for (MyService service : myServices) {
   // your code...
 }

Optionally you can pass in a RankedServices.ChangeListener instance to get notified when the list of referenced services has changed.

Since:
2.3
See Also:
  • "OSGi Compendium 6.0, Declarative Services 1.3, Reference Field Option, ยง112.3.8.1"

  • Constructor Details

    • RankedServices

      @Deprecated public RankedServices()
      Deprecated.
      Use RankedServices(Order) to explicitly give the order.
      Instantiate without change listener in ascending order (lowest service ranking first).

    • RankedServices

      @Deprecated public RankedServices(RankedServices.ChangeListener changeListener)
      Deprecated.
      Use RankedServices(Order order, ChangeListener changeListener) instead
      Instantiate with change listener in ascending order (lowest service ranking first).
      Parameters:
      changeListener - Change listener

    • RankedServices

      public RankedServices(Order order)
      Instantiate without change listener but with a given order.
      Parameters:
      order - the order in which the services should be returned in iterator() and get(). Either Order.ASCENDING or Order.DESCENDING. Use Order.DESCENDING if you want to have the service with the highest ranking returned first (this is the service which would also be chosen by BundleContext.getServiceReference(String)).
      Since:
      2.4

    • RankedServices

      public RankedServices(Order order, RankedServices.ChangeListener changeListener)
      Instantiate with change listener.
      Parameters:
      order - the order in which the services should be returned in iterator() and get(). Either Order.ASCENDING or Order.DESCENDING. Use Order.DESCENDING if you want to have the service with the highest ranking returned first (this is the service which would also be chosen by BundleContext.getServiceReference(String)).
      changeListener - Change listener
      Since:
      2.4

  • Method Details

    • bind

      public void bind(T service, Map<String,Object> props)
      Handle bind service event.
      Parameters:
      service - Service instance
      props - Service reference properties

    • unbind

      public void unbind(T service, Map<String,Object> props)
      Handle unbind service event.
      Parameters:
      service - Service instance
      props - Service reference properties

    • get

      public Collection<T> get()
      Deprecated.
      Use getList() instead
      Lists all services registered in OSGi, sorted by service ranking (either ascending or descending depending on the order given in the constructor).
      Returns:
      Collection of service instances

    • getList

      public List<T> getList()
      Lists all services registered in OSGi, sorted by service ranking (either ascending or descending depending on the order given in the constructor).
      Returns:
      List of service instances

    • iterator

      public Iterator<T> iterator()
      Iterates all services registered in OSGi, sorted by service ranking (either ascending or descending depending on the order given in the constructor).
      Specified by:
      iterator in interface Iterable<T>
      Returns:
      Iterator with service instances.