org.apache.samza.operators.functions

Interface AsyncFlatMapFunction<M,OM>

Type Parameters:

M - type of the input message

OM - type of the transformed messages

All Superinterfaces:

ClosableFunction, InitableFunction, java.io.Serializable

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@InterfaceStability.Unstable
 @FunctionalInterface
public interface AsyncFlatMapFunction<M,OM>
extends InitableFunction, ClosableFunction, java.io.Serializable

Asynchronous variant of the FlatMapFunction used in tandem with MessageStream.flatMapAsync(AsyncFlatMapFunction) to transform a collection of 0 or more messages.

Typically, AsyncFlatMapFunction is used for describing complex transformations that involve IO operations or remote calls. The following pseudo code demonstrates a sample implementation of AsyncFlatMapFunction that sends out an email and returns the status asynchronously.

 
    AsyncFlatMapFunction<Email, Status> asyncEmailSender = (Email message) -> {
        ...

        Request<Email> emailRequest = buildEmailRequest(message);
        Future<EmailResponse> emailResponseFuture = emailClient.sendRequest(emailRequest); // send email asynchronously
        ...

        return new CompletableFuture<>(emailResponseFuture)
             .thenApply(response -> fetchStatus(response);
    }
 
 

The function needs to be thread safe in case of task.max.concurrency>1. It also needs to coordinate any shared state since happens-before is not guaranteed between the messages delivered to the function. Refer to MessageStream.flatMapAsync(AsyncFlatMapFunction) docs for more details on the modes and guarantees.

For each invocation, the CompletionStage returned by the function should be completed successfully/exceptionally within task.callback.timeout.ms; failure to do so will result in SamzaException bringing down the application.

Method Summary

Modifier and Type	Method and Description
java.util.concurrent.CompletionStage<java.util.Collection<OM>>	apply(M message) Transforms the provided message into a collection of 0 or more messages.

Methods inherited from interface org.apache.samza.operators.functions.InitableFunction

init

Methods inherited from interface org.apache.samza.operators.functions.ClosableFunction

close

Method Detail

apply

java.util.concurrent.CompletionStage<java.util.Collection<OM>> apply(M message)

Transforms the provided message into a collection of 0 or more messages.

Parameters:

message - the input message to be transformed

Returns:

a CompletionStage of a Collection of transformed messages