How can we implement the SubmissionPublisher class in Java 9?

Since Java 9, we can create Reactive Streams by introducing four core interfaces: Publisher, Subscriber, Subscription, Processor, and one concrete class: SubmissionPublisher that implements the Publisher interface. Each interface plays a different role, corresponding to the principles of Reactive Streams. We can use the submit() method of SubmissionPublisher class to publish the provided item to each subscriber.

Syntax

public class SubmissionPublisher<T> extends Object implements Flow.Publisher<T>, AutoCloseable

In the below example, we can implement the SubmissionPublisher class

Example

import java.util.concurrent.Flow.Subscriber;
import java.util.concurrent.Flow.Subscription;
import java.util.concurrent.SubmissionPublisher;

class MySubscriber<T> implements Subscriber<T> {
   private Subscription subscription;
   private String name;
   public MySubscriber(String name) {
      this.name = name;
   }
   @Override
   public void onComplete() {
      System.out.println(name + ": onComplete");
   }
   @Override
   public void onError(Throwable t) {
      System.out.println(name + ": onError");
      t.printStackTrace();
   }
   @Override
   public void onNext(T msg) {
      System.out.println(name + ": " + msg.toString() + " received in onNext");
      subscription.request(1);
   }
   @Override
   public void onSubscribe(Subscription subscription) {
      System.out.println(name + ": onSubscribe");
      this.subscription = subscription;
      subscription.request(1);
   }
}

// Main class
public class FlowTest {
   public static void main(String args[]) {
      SubmissionPublisher<String> publisher = new SubmissionPublisher<>();
      MySubscriber<String> subscriber = new MySubscriber<>("Mine");
      MySubscriber<String> subscriberYours = new MySubscriber<>("Yours");
      MySubscriber<String> subscriberHis = new MySubscriber<>("His");
      MySubscriber<String> subscriberHers = new MySubscriber<>("Her");

      publisher.subscribe(subscriber);
      publisher.subscribe(subscriberYours);
      publisher.subscribe(subscriberHis);
      publisher.subscribe(subscriberHers);

      publisher.submit("One");
      publisher.submit("Two");
      publisher.submit("Three");
      publisher.submit("Four");
      publisher.submit("Five");

      try {
         Thread.sleep(1000);
      } catch(InterruptedException e) {
         e.printStackTrace();
      }
      publisher.close();
   }
}

Output

Yours: onSubscribe
His: onSubscribe
Mine: onSubscribe
His: One received in onNext
Yours: One received in onNext
Mine: One received in onNext
Yours: Two received in onNext
His: Two received in onNext
Yours: Three received in onNext
Mine: Two received in onNext
Yours: Four received in onNext
His: Three received in onNext
Yours: Five received in onNext
Mine: Three received in onNext
Her: onSubscribe
His: Four received in onNext
Her: One received in onNext
Mine: Four received in onNext
Her: Two received in onNext
His: Five received in onNext
Her: Three received in onNext
Mine: Five received in onNext
Her: Four received in onNext
Her: Five received in onNext
Yours: onComplete
His: onComplete
Mine: onComplete
Her: onComplete

raja

Updated on: 09-Mar-2020

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