Docs: examples for io streams with StreamConverters (#28746)

akka-docs/src/test/scala/docs/stream/operators/converters/ToFromJavaIOStreams.scala

@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.converters
+
+// #import
+import java.io.ByteArrayInputStream
+import java.io.ByteArrayOutputStream
+
+import akka.NotUsed
+import akka.stream.IOResult
+import akka.stream.scaladsl.Flow
+import akka.stream.scaladsl.Sink
+import akka.stream.scaladsl.Source
+import akka.stream.scaladsl.StreamConverters
+import akka.util.ByteString
+// #import
+import akka.testkit.AkkaSpec
+import org.scalatest.concurrent.Futures
+
+import scala.concurrent.Future
+
+class ToFromJavaIOStreams extends AkkaSpec with Futures {
+
+  "demonstrate conversion from java.io.streams" in {
+
+    //#tofromJavaIOStream
+    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)
+
+    //#tofromJavaIOStream
+    whenReady(eventualResult) { _ =>
+      outputStream.toByteArray.map(_.toChar).mkString should be("SOME RANDOM INPUT")
+    }
+
+  }
+
+}