Flow API (java.util.concurrent.Flow) has introduced in Java 9. It helps to understand different ways in which the Publisher and Subscriber interfaces interact to perform desired operations.
Flow API consists of Publisher, Subscriber, Subscription, and Processor interfaces, which can be based on reactive stream specification.
In the below example, we can implement Flow API by using Publisher-Subscriber interfaces.
Example
import java.util.concurrent.Flow.Publisher; import java.util.concurrent.Flow.Subscriber; import java.util.concurrent.Flow.Subscription; public class FlowAPITest { public static void main(String args[]) { Publisher<Integer> publisherSync = new Publisher<Integer>() { // Create publisher @Override public void subscribe(Subscriber<? super Integer> subscriber) { for(int i = 0; i < 10; i++) { System.out.println(Thread.currentThread().getName() + " | Publishing = " + i); subscriber.onNext(i); } subscriber.onComplete(); } }; Subscriber<Integer> subscriberSync = new Subscriber<Integer>() { // Create subscriber @Override public void onSubscribe(Subscription subscription) { } @Override public void onNext(Integer item) { System.out.println(Thread.currentThread().getName() + " | Received = " + item); try { Thread.sleep(100); } catch(InterruptedException e) { e.printStackTrace(); } } @Override public void onError(Throwable throwable) { } @Override public void onComplete() { } }; publisherSync.subscribe(subscriberSync); } }
Output
main | Publishing = 0 main | Received = 0 main | Publishing = 1 main | Received = 1 main | Publishing = 2 main | Received = 2 main | Publishing = 3 main | Received = 3 main | Publishing = 4 main | Received = 4 main | Publishing = 5 main | Received = 5 main | Publishing = 6 main | Received = 6 main | Publishing = 7 main | Received = 7 main | Publishing = 8 main | Received = 8 main | Publishing = 9 main | Received = 9