Add stream-substream.md #23461

akka-docs/src/test/java/jdocs/stream/SubstreamDocTest.java

@@ -0,0 +1,115 @@
+/**
+ *  Copyright (C) 2015-2017 Lightbend Inc. <http://www.lightbend.com/>
+ */
+package jdocs.stream;
+
+import akka.actor.ActorSystem;
+import akka.stream.ActorMaterializer;
+import akka.stream.Materializer;
+import akka.stream.javadsl.Sink;
+import akka.stream.javadsl.Source;
+import akka.testkit.javadsl.TestKit;
+import jdocs.AbstractJavaTest;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+public class SubstreamDocTest  extends AbstractJavaTest {
+
+    static ActorSystem system;
+    static Materializer mat;
+
+    @BeforeClass
+    public static void setup() {
+        system = ActorSystem.create("FlowDocTest");
+        mat = ActorMaterializer.create(system);
+    }
+
+    @AfterClass
+    public static void tearDown() {
+        TestKit.shutdownActorSystem(system);
+        system = null;
+        mat = null;
+    }
+
+    @Test
+    public void demonstrateGroupBy() throws Exception {
+        //#groupBy1
+        Source.from(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+          .groupBy(3, elem -> elem % 3);
+        //#groupBy1
+
+        //#groupBy2
+        Source.from(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+          .groupBy(3, elem -> elem % 3)
+          .to(Sink.ignore())
+          .run(mat);
+        //#groupBy2
+
+        //#groupBy3
+        Source.from(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+          .groupBy(3, elem -> elem % 3)
+          .mergeSubstreams()
+          .runWith(Sink.ignore(), mat);
+        //#groupBy3
+
+        //#groupBy4
+        Source.from(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+          .groupBy(3, elem -> elem % 3)
+          .mergeSubstreamsWithParallelism(2)
+          .runWith(Sink.ignore(), mat);
+        //concatSubstreams is equivalent to mergeSubstreamsWithParallelism(1)
+        Source.from(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+          .groupBy(3, elem -> elem % 3)
+          .concatSubstreams()
+          .runWith(Sink.ignore(), mat);
+        //#groupBy4
+    }
+
+    @Test
+    public void demonstrateSplitWhenAfter() throws Exception {
+        //#splitWhenAfter
+        Source.from(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+          .splitWhen(elem -> elem == 3);
+
+        Source.from(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+          .splitAfter(elem -> elem == 3);
+        //#splitWhenAfter
+
+        //#wordCount
+        String text =
+          "This is the first line.\n" +
+          "The second line.\n" +
+          "There is also the 3rd line\n";
+
+        Source.from(Arrays.asList(text.split("")))
+          .map(x -> x.charAt(0))
+          .splitAfter(x -> x == '\n')
+          .filter(x -> x != '\n')
+          .map(x -> 1)
+          .reduce((x,y) -> x + y)
+          .to(Sink.foreach(x -> System.out.println(x)))
+          .run(mat);
+        //#wordCount
+        Thread.sleep(1000);
+    }
+
+    @Test
+    public void demonstrateflatMapConcatMerge() throws Exception {
+        //#flatMapConcat
+        Source.from(Arrays.asList(1, 2))
+          .flatMapConcat(i -> Source.from(Arrays.asList(i, i, i)))
+          .runWith(Sink.ignore(), mat);
+        //#flatMapConcat
+
+        //#flatMapMerge
+        Source.from(Arrays.asList(1, 2))
+          .flatMapMerge(2, i -> Source.from(Arrays.asList(i, i, i)))
+          .runWith(Sink.ignore(), mat);
+        //#flatMapMerge
+    }
+}