StreamConverters.fromOutputStream

Create a sink that wraps an OutputStream.

Additional Sink and Source converters

Signature

StreamConverters.fromOutputStreamStreamConverters.fromOutputStream

Description

Creates a Sink which writes incoming ByteStringByteStrings to a java.io.OutputStream created by the given function.

Materializes a CompletionStageFuture of IOResult that will be completed with the size of the file (in bytes) on completion, and a possible exception if IO operation was not completed successfully.

You can configure the default dispatcher for this Source by changing the akka.stream.materializer.blocking-io-dispatcher or set it for a given Source by using akka.stream.ActorAttributes.

If autoFlush is true the OutputStream will be flushed whenever a byte array is written, defaults to false. The OutputStream will be closed when the stream flowing into this Sink is completed. The Sink will cancel the stream when the OutputStream is no longer writable.

See also fromInputStream

Example

Here is an example using both fromInputStream and fromOutputStream to read from a java.io.InputStream, uppercase the read content and write back out into a java.io.OutputStream.

Scala
val bytes = "Some random input".getBytes
val inputStream = new ByteArrayInputStream(bytes)
val outputStream = new ByteArrayOutputStream()

val source: Source[ByteString, Future[IOResult]] = StreamConverters.fromInputStream(() => inputStream)

val toUpperCase: Flow[ByteString, ByteString, NotUsed] = Flow[ByteString].map(_.map(_.toChar.toUpper.toByte))

val sink: Sink[ByteString, Future[IOResult]] = StreamConverters.fromOutputStream(() => outputStream)

val eventualResult = source.via(toUpperCase).runWith(sink)
Java
java.io.InputStream inputStream = new ByteArrayInputStream(bytes);
Source<ByteString, CompletionStage<IOResult>> source =
    StreamConverters.fromInputStream(() -> inputStream);

// Given a ByteString produces a ByteString with the upperCase representation
// Removed from the sample for brevity.
// Flow<ByteString, ByteString, NotUsed> toUpperCase = ...

java.io.OutputStream outputStream = new ByteArrayOutputStream();
Sink<ByteString, CompletionStage<IOResult>> sink =
    StreamConverters.fromOutputStream(() -> outputStream);

CompletionStage<IOResult> ioResultCompletionStage =
    source.via(toUpperCase).runWith(sink, system);
// When the ioResultCompletionStage completes, the byte array backing the outputStream
// will contain the uppercase representation of the bytes read from the inputStream.
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