concatLazy

After completion of the original upstream the elements of the given source will be emitted.

Fan-in operators

Signature

Source.concatSource.concat Flow.concatFlow.concat

Description

After completion of the original upstream the elements of the given source will be emitted.

Both streams will be materialized together, however, the given stream will be pulled for the first time only after the original upstream was completed. (In contrast, concat, introduces single-element buffers after both, original and given sources so that the given source is also pulled once immediately.)

To defer the materialization of the given source (or to completely avoid its materialization if the original upstream fails or cancels), wrap it into Source.lazySource.

If materialized values needs to be collected concatLazyMat is available.

Example

Scala

copysourceval sourceA = Source(List(1, 2, 3, 4))
val sourceB = Source(List(10, 20, 30, 40))

sourceA.concatLazy(sourceB).runWith(Sink.foreach(println))

Java

copysourceimport org.apache.pekko.stream.javadsl.Keep;
import org.apache.pekko.stream.javadsl.Source;
import org.apache.pekko.stream.javadsl.Sink;

import java.util.*;

Source<Integer, NotUsed> sourceA = Source.from(Arrays.asList(1, 2, 3, 4));
Source<Integer, NotUsed> sourceB = Source.from(Arrays.asList(10, 20, 30, 40));
sourceA.concatLazy(sourceB).runForeach(System.out::println, system);
// prints 1, 2, 3, 4, 10, 20, 30, 40

Reactive Streams semantics