Package org.apache.pekko.actor.typed.pubsub

Class Topic

java.lang.Object

org.apache.pekko.actor.typed.pubsub.Topic

public class Topic
extends Object

A pub sub topic is an actor that handles subscribing to a topic and publishing messages to all subscribed actors.

It is mostly useful in a clustered setting, where it is intended to be started once on every node that want to house subscribers or publish messages to the topic, but it also works in a local setting without cluster.

In a clustered context messages are deduplicated so that there is at most one message sent to each node for each publish and if there are no subscribers on a node, no message is sent to it. Note that the list of subscribers is eventually consistent and there are no delivery guarantees built in.

Each topic results in a pekko.actor.typed.receptionist.ServiceKey in the pekko.actor.typed.receptionist.Receptionist so the same scaling recommendation holds for topics, see docs: https://pekko.apache.org/docs/pekko/current/typed/actor-discovery.html#receptionist-scalability

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	Topic.Command<T>	Not for user extension
static class	Topic.GetTopicStats$	Scala API: Get a summary of the state for a local topic actor.
static class	Topic.Publish$	Scala API: Publish the message to all currently known subscribers.
static class	Topic.Subscribe$	Scala API: Subscribe to this topic.
static interface	Topic.TopicStats	Response to the GetTopicStats query.
static class	Topic.Unsubscribe$	Scala API: Unsubscribe a previously subscribed actor from this topic.

Constructor Summary

Constructors

Constructor	Description
Topic()

Method Summary

Modifier and Type	Method	Description
static <T> Behavior<Topic.Command<T>>	apply(String topicName, scala.reflect.ClassTag<T> classTag)	Scala API: Create a topic actor behavior for the given topic name and message type.
static <T> Behavior<Topic.Command<T>>	create(Class<T> messageClass, String topicName)	Java API: Create a topic actor behavior for the given topic name and message class
static <T> Topic.Command<T>	getTopicStats(ActorRef<Topic.TopicStats> replyTo)	Java API: Get a summary of the state for a local topic actor.
static <T> Topic.Command<T>	publish(T message)	Java API: Publish the message to all currently known subscribers.
static <T> Topic.Command<T>	subscribe(ActorRef<T> subscriber)	Java API: Subscribe to this topic.
static <T> Topic.Command<T>	unsubscribe(ActorRef<T> subscriber)	Java API: Unsubscribe a previously subscribed actor from this topic.

Methods inherited from class java.lang.Object

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

Constructor Details

Topic

public Topic()

Method Details

publish

public static <T> Topic.Command<T> publish(T message)

Java API: Publish the message to all currently known subscribers.

subscribe

public static <T> Topic.Command<T> subscribe(ActorRef<T> subscriber)

Java API: Subscribe to this topic. Should only be used for local subscribers.

getTopicStats

public static <T> Topic.Command<T> getTopicStats(ActorRef<Topic.TopicStats> replyTo)

Java API: Get a summary of the state for a local topic actor.

See Topic.TopicStats for caveats

unsubscribe

public static <T> Topic.Command<T> unsubscribe(ActorRef<T> subscriber)

Java API: Unsubscribe a previously subscribed actor from this topic.

apply

public static <T> Behavior<Topic.Command<T>> apply(String topicName,
 scala.reflect.ClassTag<T> classTag)

Scala API: Create a topic actor behavior for the given topic name and message type.

create

public static <T> Behavior<Topic.Command<T>> create(Class<T> messageClass,
 String topicName)

Java API: Create a topic actor behavior for the given topic name and message class