Flow API is official support for reactive streams specification since Java 9. It is a combination of both Iterator and Observer patterns. The Flow API is an interoperation specification and not an end-user API like RxJava.
Flow API consists of four basic interfaces:
- Subscriber: The Subscriber subscribes to Publisher for callbacks.
- Publisher: The Publisher publishes the stream of data items to the registered subscribers.
- Subscription: The link between publisher and subscriber.
- Processor: The processor sits between Publisher and Subscriber, and transforms one stream to another.
In the below example, we have created a basic subscriber that asks for one data object, prints it and asks for one more. We can use a publisher implementation provided by Java (SubmissionPublisher) to complete our session.
Example
import java.util.concurrent.Flow; import java.util.List; import java.util.concurrent.SubmissionPublisher; class MySubscriber<T>implements Flow.Subscriber<T> { private Flow.Subscription subscription; @Override public void onSubscribe(Flow.Subscription subscription) { this.subscription = subscription; this.subscription.request(1); } @Override public void onNext(T item) { System.out.println(item); subscription.request(1); } @Override public void onError(Throwable throwable) { throwable.printStackTrace(); } @Override public void onComplete() { System.out.println("Done"); } } // main class public class FlowTest { public static void main(String args[]) { List<String> items = List.of("1", "2", "3", "4", "5", "6", "7", "8", "9", "10"); SubmissionPublisher<String> publisher = new SubmissionPublisher<>(); publisher.subscribe(new MySubscriber<>()); items.forEach(s -> { try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } publisher.submit(s); }); publisher.close(); } }
Output
1 2 3 4 5 6 7 8 9 10 Done