added break mechanisms for Stream.forEach (#7053)

java-streams-2/pom.xml

@@ -4,7 +4,7 @@
     <groupId>com.baeldung.javastreams2</groupId>
     <artifactId>javastreams2</artifactId>
     <version>1.0</version>
-    <name>Stream Reduce</name>
+    <name>javastreams2</name>
     <packaging>jar</packaging>
 
     <parent>
@@ -42,8 +42,8 @@
 	
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <maven.compiler.source>1.8</maven.compiler.source>
-        <maven.compiler.target>1.8</maven.compiler.target>
+        <maven.compiler.source>1.9</maven.compiler.source>
+        <maven.compiler.target>1.9</maven.compiler.target>
         <assertj.version>3.11.1</assertj.version>
     </properties>
 </project>

java-streams-2/src/main/java/com/baeldung/breakforeach/CustomForEach.java

@@ -0,0 +1,32 @@
+package com.baeldung.breakforeach;
+
+import java.util.Spliterator;
+import java.util.function.BiConsumer;
+import java.util.stream.Stream;
+
+public class CustomForEach {
+
+    public static class Breaker {
+        private boolean shouldBreak = false;
+
+        public void stop() {
+            shouldBreak = true;
+        }
+
+        boolean get() {
+            return shouldBreak;
+        }
+    }
+
+    public static <T> void forEach(Stream<T> stream, BiConsumer<T, Breaker> consumer) {
+        Spliterator<T> spliterator = stream.spliterator();
+        boolean hadNext = true;
+        Breaker breaker = new Breaker();
+
+        while (hadNext && !breaker.get()) {
+            hadNext = spliterator.tryAdvance(elem -> {
+                consumer.accept(elem, breaker);
+            });
+        }
+    }
+}

java-streams-2/src/main/java/com/baeldung/breakforeach/CustomSpliterator.java

@@ -0,0 +1,31 @@
+package com.baeldung.breakforeach;
+
+import java.util.Spliterator;
+import java.util.Spliterators;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+
+public class CustomSpliterator<T> extends Spliterators.AbstractSpliterator<T> {
+
+    private Spliterator<T> splitr;
+    private Predicate<T> predicate;
+    private boolean isMatched = true;
+
+    public CustomSpliterator(Spliterator<T> splitr, Predicate<T> predicate) {
+        super(splitr.estimateSize(), 0);
+        this.splitr = splitr;
+        this.predicate = predicate;
+    }
+
+    @Override
+    public boolean tryAdvance(Consumer<? super T> consumer) {
+        boolean hadNext = splitr.tryAdvance(elem -> {
+            if (predicate.test(elem) && isMatched) {
+                consumer.accept(elem);
+            } else {
+                isMatched = false;
+            }
+        });
+        return hadNext && isMatched;
+    }
+}

java-streams-2/src/main/java/com/baeldung/breakforeach/CustomTakeWhile.java

@@ -0,0 +1,14 @@
+package com.baeldung.breakforeach;
+
+import java.util.function.Predicate;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+public class CustomTakeWhile {
+
+    public static <T> Stream<T> takeWhile(Stream<T> stream, Predicate<T> predicate) {
+        CustomSpliterator<T> customSpliterator = new CustomSpliterator<>(stream.spliterator(), predicate);
+        return StreamSupport.stream(customSpliterator, false);
+    }
+
+}

java-streams-2/src/main/java/com/baeldung/breakforeach/TakeWhileExample.java

@@ -0,0 +1,26 @@
+package com.baeldung.breakforeach;
+
+import java.util.List;
+import java.util.stream.Stream;
+
+import static java.util.Arrays.asList;
+
+public class TakeWhileExample {
+
+    public static void takeWhileJava9() {
+        Stream.of("cat", "dog", "elephant", "fox", "rabbit", "duck")
+            .takeWhile(n -> n.length() % 2 != 0)
+            .forEach(System.out::println); // cat, dog
+    }
+
+    public static void plainForLoopWithBreak() {
+        List<String> list = asList("cat", "dog", "elephant", "fox", "rabbit", "duck");
+        for (int i = 0; i < list.size(); i++) {
+            String item = list.get(i);
+            if (item.length() % 2 == 0) {
+                break;
+            }
+            System.out.println(item);
+        }
+    }
+}

java-streams-2/src/test/java/com/baeldung/breakforeach/BreakFromStreamForEachUnitTest.java

@@ -0,0 +1,41 @@
+package com.baeldung.breakforeach;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static java.util.Arrays.asList;
+import static org.junit.Assert.assertEquals;
+
+public class BreakFromStreamForEachUnitTest {
+
+    @Test
+    public void whenCustomTakeWhileIsCalled_ThenCorrectItemsAreReturned() {
+        Stream<String> initialStream = Stream.of("cat", "dog", "elephant", "fox", "rabbit", "duck");
+
+        List<String> result = CustomTakeWhile.takeWhile(initialStream, x -> x.length() % 2 != 0)
+                .collect(Collectors.toList());
+
+        assertEquals(asList("cat", "dog"), result);
+    }
+
+    @Test
+    public void whenCustomForEachIsCalled_ThenCorrectItemsAreReturned() {
+        Stream<String> initialStream = Stream.of("cat", "dog", "elephant", "fox", "rabbit", "duck");
+        List<String> result = new ArrayList<>();
+
+        CustomForEach.forEach(initialStream, (elem, breaker) -> {
+            if (elem.length() % 2 == 0) {
+                breaker.stop();
+            } else {
+                result.add(elem);
+            }
+        });
+
+        assertEquals(asList("cat", "dog"), result);
+    }
+
+}

pom.xml

@@ -464,7 +464,7 @@
                 <module>java-rmi</module>
                 <module>java-spi</module>
                 <module>java-streams</module>
-                <module>java-streams-2</module>
+                <!-- <module>java-streams-2</module> --> <!-- We haven't upgraded to java 9. Fixing in BAEL-10841 -->
                 <module>java-strings</module>
                 <module>java-strings-2</module>
                 <module>java-vavr-stream</module>