Added an example on the JDK 9 Flow API (session 5).

Author: martinfmi

session-5-reactive-api/01_Create_subscriber/README.md

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+### Implementing the reactive programming API
+
+In this example we are going to demonstrate how does the `java.util.concurrent.Flow` API work in general. For that purpose we are going to create an implementation of the `java.util.concurrent.Flow.Subscriber` interface (`com.project.DefaultSubscriber`) and register a concrete subscriber to a given `java.util.concurrent.Flow.Publisher` instance. The flow publisher is an instance of the `java.util.concurrent.SubmissionPublisher` class provided by JDK 9 that implements the `java.util.concurrent.Flow.Publisher` API.
+
+In the source folder there is a `PrimeNumberSubscriber` project that provides a stub implementation of the subscriber and demo for the publisher. 
+
+Add implementation of the onNext() and onSubscribe() methods accordingly. The onNext() method should check if the passed number is prime or not and print the result on the standard output. Then create an instance of the `com.project.DefaultSubscriber` class and register it to the publisher created in the `com.project.Main` class.
+
+Use the `compile.sh` script to compile the project:
+
+ $ ./compile.sh
+
+Run the compiled `com.project.Main` class with the `run.sh` script:
+ 
+ $ ./run.sh

session-5-reactive-api/01_Create_subscriber/compile.sh

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+#!/bin/bash
+
+set -eu
+
+javac -d src/PrimeNumberSubscriber/target/classes \
+ src/PrimeNumberSubscriber/com/project/*.java
+ 

session-5-reactive-api/01_Create_subscriber/run.sh

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+#!/bin/bash
+
+set -eu
+
+java -cp src/PrimeNumberSubscriber/target/classes com.project.Main

session-5-reactive-api/01_Create_subscriber/src/PrimeNumberSubscriber/com/project/DefaultSubscriber.java

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+package com.project;
+
+import java.util.concurrent.Flow.Subscriber;
+import java.util.concurrent.Flow.Subscription;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public class DefaultSubscriber implements Subscriber<Integer>{
+
+private static final Logger LOGGER = Logger.getLogger(DefaultSubscriber.class.getName());
+
+private Subscription subscription;
+
+@Override
+public void onComplete() {
+LOGGER.info("COMPLETED");
+}
+
+@Override
+public void onError(Throwable t) {
+LOGGER.log(Level.SEVERE, t.getMessage(), t);
+}
+
+@Override
+public void onNext(Integer number) {
+// TODO
+}
+
+@Override
+public void onSubscribe(Subscription subscription) {
+// TODO
+}
+}

session-5-reactive-api/01_Create_subscriber/src/PrimeNumberSubscriber/com/project/Main.java

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+package com.project;
+
+import java.util.Arrays;
+import java.util.concurrent.SubmissionPublisher;
+import java.util.logging.Logger;
+
+public class Main {
+
+private static final Logger LOGGER = Logger.getLogger(Main.class.getName());
+
+public static void main(String[] args) throws InterruptedException {
+
+LOGGER.info("Checking prime numbers ...");
+ SubmissionPublisher<Integer> publisher = new SubmissionPublisher<>(); 
+ 
+ // TODO: create subscriber
+ 
+ Integer[] numbers = {4, 17, 19, 101, 105, 107, 201}; 
+ 
+ Arrays.asList(numbers).stream().forEach(i -> publisher.submit(i));
+ 
+ // add some wait time ...
+ Thread.sleep(3000);
+ publisher.close();
+}
+}