com.lightbend.lagom.javadsl.pubsub

Class PubSubRef<T>

Object

com.lightbend.lagom.javadsl.pubsub.PubSubRef<T>

All Implemented Interfaces:

akka.actor.NoSerializationVerificationNeeded

public final class PubSubRef<T>
extends Object
implements akka.actor.NoSerializationVerificationNeeded

A PubSubRef represents a publish/subscribe topic.

Messages can be published to the topic via a stream by using the Source returned by the publisher() method. A single message can be published with the publish(T) method.

Messages can be consumed from the topic via a stream by using the Sink returned by the subscriber() method.

The registry of subscribers is eventually consistent, i.e. new subscribers are not immediately visible at other nodes, but typically the information will be fully replicated to all other nodes after a few seconds.

New subscribers will not see old messages that were published to the topic, i.e. it is only a live stream of messages.

Messages are not guaranteed to be delivered, i.e. they may be lost. That can for example happen if there is a transient network partition.

The subscriber has a buffer of received messages, but messages will be dropped if that buffer is full and demand for more elements have not been requested from downstream. This can happen if a subscriber is slower than the publishers of the messages. When the buffer is full the oldest messages are dropped to make room for new messages.

Constructor Summary

Constructors

Constructor and Description
PubSubRef(TopicId<T> topic, akka.actor.ActorRef mediator, akka.actor.ActorSystem system, int bufferSize)

Method Summary

Modifier and Type	Method and Description
CompletionStage<Boolean>	hasAnySubscribers() Request if this topic has any known subscribers at this point.
void	publish(T message)
akka.stream.javadsl.Sink<T,akka.NotUsed>	publisher() Publish messages from a stream to the topic.
akka.stream.javadsl.Source<T,akka.NotUsed>	subscriber() Consume messages from the topic via a stream.
TopicId<T>	topic()
String	toString()

Methods inherited from class Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

PubSubRef

public PubSubRef(TopicId<T> topic,
                 akka.actor.ActorRef mediator,
                 akka.actor.ActorSystem system,
                 int bufferSize)

Method Detail

hasAnySubscribers

public CompletionStage<Boolean> hasAnySubscribers()

Request if this topic has any known subscribers at this point. The CompletionStage is completed with the currently known information at this node, i.e. completion is not deferred until there are subscribers.

Note that the registry of subscribers is eventually consistent, i.e. new subscribers are not immediately visible at other nodes, but typically the information will be fully replicated to all other nodes after a few seconds.

This method is especially useful when writing tests that require that a subscriber is known before sending messages to a topic.

publish

public void publish(T message)

publisher

public akka.stream.javadsl.Sink<T,akka.NotUsed> publisher()

Publish messages from a stream to the topic. You have to connect a Source that produces the messages to this Sink and then run the stream.

subscriber

public akka.stream.javadsl.Source<T,akka.NotUsed> subscriber()

Consume messages from the topic via a stream. You can return this Source as a response in a ServiceCall and the elements will be streamed to the client. Otherwise you have to connect a Sink that consumes the messages from this Source and then run the stream.

toString

public String toString()

Overrides:

toString in class Object

topic

public TopicId<T> topic()