Java 9 supports to create Reactive Streams by introducing a few interfaces: Publisher, Subscriber, Subscription, and SubmissionPublisher class that implements the Publisher interface. Each interface can play a different role corresponding to the principles of Reactive Streams.
We can use the Subscriber interface to subscribe to the data that is being published by a publisher. We need to implement the Subscriber interface and provide an implementation for the abstract methods.
Flow.Subscriber interface methods:
- onComplete(): This method has been called when the Publisher object completes its role.
- onError(): This method has been called when something goes wrong in Publisher and is notified to the Subscriber.
- onNext(): This method has been called whenever Publisher has new information to be notified to all Subscribers.
- onSubscribe(): This method has been called when Publisher adds Subscriber.
Example
import java.util.concurrent.Flow;
import java.util.concurrent.SubmissionPublisher;
import java.util.stream.IntStream;
public class SubscriberImplTest {
public static class Subscriber implements Flow.Subscriber<Integer> {
private Flow.Subscription subscription;
private boolean isDone;
@Override
public void onSubscribe(Flow.Subscription subscription) {
System.out.println("Subscribed");
this.subscription = subscription;
this.subscription.request(1);
}
@Override
public void onNext(Integer item) {
System.out.println("Processing " + item);
this.subscription.request(1);
}
@Override
public void onError(Throwable throwable) {
throwable.printStackTrace();
}
@Override
public void onComplete() {
System.out.println("Processing done");
isDone = true;
}
}
public static void main(String args[]) throws InterruptedException {
SubmissionPublisher<Integer> publisher = new SubmissionPublisher<>();
Subscriber subscriber = new Subscriber();
publisher.subscribe(subscriber);
IntStream intData = IntStream.rangeClosed(1, 10);
intData.forEach(publisher::submit);
publisher.close();
while(!subscriber.isDone) {
Thread.sleep(10);
}
System.out.println("Done");
}
}Output
Subscribed Processing 1 Processing 2 Processing 3 Processing 4 Processing 5 Processing 6 Processing 7 Processing 8 Processing 9 Processing 10 Processing done Done