BAEL-679 code for reactive streams (#1970)

* BAEL-679 code for reactive streams

* BAEL-679 typo

core-java-9/src/main/java/com/baeldung/java9/streams.reactive/EndSubscriber.java

@@ -0,0 +1,43 @@
+package com.baeldung.java9.streams.reactive;
+
+import java.util.LinkedList;
+import java.util.List;
+import java.util.concurrent.Flow.Subscriber;
+import java.util.concurrent.Flow.Subscription;
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class EndSubscriber<T> implements Subscriber<T> {
+    private final AtomicInteger howMuchMessagesToConsume;
+    private Subscription subscription;
+    public List<T> consumedElements = new LinkedList<>();
+
+    public EndSubscriber(Integer howMuchMessagesToConsume) {
+        this.howMuchMessagesToConsume = new AtomicInteger(howMuchMessagesToConsume);
+    }
+
+    @Override
+    public void onSubscribe(Subscription subscription) {
+        this.subscription = subscription;
+        subscription.request(1);
+    }
+
+    @Override
+    public void onNext(T item) {
+        howMuchMessagesToConsume.decrementAndGet();
+        System.out.println("Got : " + item);
+        consumedElements.add(item);
+        if (howMuchMessagesToConsume.get() > 0) {
+            subscription.request(1);
+        }
+    }
+
+    @Override
+    public void onError(Throwable t) {
+        t.printStackTrace();
+    }
+
+    @Override
+    public void onComplete() {
+        System.out.println("Done");
+    }
+}

core-java-9/src/main/java/com/baeldung/java9/streams.reactive/TransformProcessor.java

@@ -0,0 +1,38 @@
+package com.baeldung.java9.streams.reactive;
+
+import java.util.concurrent.Flow;
+import java.util.concurrent.SubmissionPublisher;
+import java.util.function.Function;
+
+public class TransformProcessor<T, R> extends SubmissionPublisher<R> implements Flow.Processor<T, R> {
+
+    private Function<T, R> function;
+    private Flow.Subscription subscription;
+
+    public TransformProcessor(Function<T, R> function) {
+        super();
+        this.function = function;
+    }
+
+    @Override
+    public void onSubscribe(Flow.Subscription subscription) {
+        this.subscription = subscription;
+        subscription.request(1);
+    }
+
+    @Override
+    public void onNext(T item) {
+        submit(function.apply(item));
+        subscription.request(1);
+    }
+
+    @Override
+    public void onError(Throwable t) {
+        t.printStackTrace();
+    }
+
+    @Override
+    public void onComplete() {
+        close();
+    }
+}