Class ExtensionId<T extends Extension>
- java.lang.Object
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- org.apache.pekko.actor.typed.ExtensionId<T>
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- Type Parameters:
T
- The concrete extension type
- Direct Known Subclasses:
ActorFlightRecorder$
,ActorRefResolver$
,Cluster$
,ClusterSharding$
,ClusterSingleton$
,DistributedData$
,DistributedData$
,EventStreamExtension$
,Receptionist$
,ReplicatedShardingExtension$
,ShardedDaemonProcess$
public abstract class ExtensionId<T extends Extension> extends java.lang.Object
Identifier and factory for an extension. Is used to look up an extension from theActorSystem
, and possibly create an instance if no instance was already registered. The extension can also be listed in the actor system configuration to have it eagerly loaded and registered on actor system startup.*Scala API*
The
ExtensionId
for an extension written in Scala is best done by letting it be the companion object of the extension. If the extension will be used from Java special care needs to be taken to provide aget
method with the concrete extension type as return (as this will not be inferred correctly by the Java compiler with the default implementation)Example:
object MyExt extends ExtensionId[Ext] { override def createExtension(system: ActorSystem[_]): MyExt = new MyExt(system) // Java API: retrieve the extension instance for the given system. def get(system: ActorSystem[_]): MyExt = apply(system) } class MyExt(system: ActorSystem[_]) extends Extension { ... } // can be loaded eagerly on system startup through configuration // note that the name is the JVM/Java class name, with a dollar sign in the end // and not the Scala object name pekko.actor.typed.extensions = ["com.example.MyExt$"] // Allows access like this from Scala MyExt().someMethodOnTheExtension() // and from Java MyExt.get(system).someMethodOnTheExtension()
*Java API*
To implement an extension in Java you should first create an
ExtensionId
singleton by implementing a static method calledgetInstance
, this is needed to be able to list the extension among thepekko.actor.typed.extensions
in the configuration and have it loaded when the actor system starts up.public class MyExt extends AbstractExtensionId<MyExtImpl> { // single instance of the identifier private final static MyExt instance = new MyExt(); // protect against other instances than the singleton private MyExt() {} // This static method singleton accessor is needed to be able to enable the extension through config when // implementing extensions in Java. public static MyExt getInstance() { return instance; } public MyExtImpl createExtension(ActorSystem<?> system) { return new MyExtImpl(); } // convenience accessor public static MyExtImpl get(ActorSystem<?> system) { return instance.apply(system); } } public class MyExtImpl implements Extension { ... } // can be loaded eagerly on system startup through configuration pekko.actor.typed.extensions = ["com.example.MyExt"] // Allows access like this from Scala MyExt.someMethodOnTheExtension() // and from Java MyExt.get(system).someMethodOnTheExtension()
For testing purposes extensions typically provide a concrete
ExtensionSetup
that can be used inpekko.actor.setup.ActorSystemSetup
when starting theActorSystem
to replace the default implementation of the extension.- See Also:
ExtensionSetup
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Constructor Summary
Constructors Constructor Description ExtensionId()
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description T
apply(ActorSystem<?> system)
Lookup or create an instance of the extension identified by this id.abstract T
createExtension(ActorSystem<?> system)
Create the extension, will be invoked at most one time per actor system where the extension is registered.boolean
equals(java.lang.Object other)
int
hashCode()
ExtensionId<T>
id()
Java API: The identifier of the extension
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Method Detail
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apply
public final T apply(ActorSystem<?> system)
Lookup or create an instance of the extension identified by this id.
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createExtension
public abstract T createExtension(ActorSystem<?> system)
Create the extension, will be invoked at most one time per actor system where the extension is registered.
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equals
public final boolean equals(java.lang.Object other)
- Overrides:
equals
in classjava.lang.Object
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hashCode
public final int hashCode()
- Overrides:
hashCode
in classjava.lang.Object
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id
public ExtensionId<T> id()
Java API: The identifier of the extension
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