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How to implement reactive streams using Flow API in Java 9?
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
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Updated on: 27-Mar-2020
2K+ Views
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