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:

java.lang.Iterable<T>

@ProviderType
public final class RankedServices<T>
extends java.lang.Object
implements java.lang.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, §112.3.8.1"

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	RankedServices.ChangeListener Notification for changes on services list.

Constructor Summary

Constructors

Constructor and Description
RankedServices() Deprecated. Use RankedServices(Order) to explicitly give the order.
RankedServices(Order order) Instantiate without change listener but with a given order.
RankedServices(Order order, RankedServices.ChangeListener changeListener) Instantiate with change listener.
RankedServices(RankedServices.ChangeListener changeListener) Deprecated. Use RankedServices(Order order, ChangeListener changeListener) instead

Method Summary

Modifier and Type	Method and Description
void	bind(T service, java.util.Map<java.lang.String,java.lang.Object> props) Handle bind service event.
java.util.Collection<T>	get() Deprecated. Use getList() instead
java.util.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).
java.util.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).
void	unbind(T service, java.util.Map<java.lang.String,java.lang.Object> props) Handle unbind service event.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Constructor Detail

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 Detail

bind

public void bind(T service,
                 java.util.Map<java.lang.String,java.lang.Object> props)

Handle bind service event.

Parameters:

service - Service instance

props - Service reference properties

unbind

public void unbind(T service,
                   java.util.Map<java.lang.String,java.lang.Object> props)

Handle unbind service event.

Parameters:

service - Service instance

props - Service reference properties

get

public java.util.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 java.util.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 java.util.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 java.lang.Iterable<T>

Returns:

Iterator with service instances.