Java : Flow (Reactive Streams) with Examples
December 5, 2023 
November 29, 2023
Flow (Java SE 20 & JDK 20) with Examples.
You will find code examples on most Flow methods.
Summary
Interrelated interfaces and static methods for establishing flow-controlled components in which Publishers produce items consumed by one or more Subscribers, each managed by a Subscription.
Please see also : Reactive Streams
class MySubscriber implements Flow.Subscriber<String> {
private Flow.Subscription subscription;
@Override
public void onSubscribe(Flow.Subscription subscription) {
System.out.printf(" onSubscribe (tid=%d)%n",
Thread.currentThread().threadId());
this.subscription = subscription;
subscription.request(1);
}
@Override
public void onNext(String item) {
System.out.printf(" onNext (tid=%d) : %s%n",
Thread.currentThread().threadId(), item);
subscription.request(1);
}
@Override
public void onError(Throwable throwable) {
System.out.printf(" onError (tid=%d) : %s%n",
Thread.currentThread().threadId(), throwable);
}
@Override
public void onComplete() {
System.out.printf(" onComplete (tid=%d)%n",
Thread.currentThread().threadId());
}
}
System.out.printf("main (tid=%d)%n", Thread.currentThread().threadId());
try (final var publisher = new SubmissionPublisher<String>()) {
System.out.println("-- subscribe --");
publisher.subscribe(new MySubscriber());
TimeUnit.SECONDS.sleep(1);
System.out.println("-- submit --");
publisher.submit("abc");
publisher.submit("123");
publisher.submit("XYZ");
TimeUnit.SECONDS.sleep(1);
System.out.println("-- close --");
}
// Result
// ↓
//main (tid=1)
//-- subscribe --
// onSubscribe (tid=32)
//-- submit --
// onNext (tid=32) : abc
// onNext (tid=32) : 123
// onNext (tid=32) : XYZ
//-- close --
// onComplete (tid=32)
Methods
static int defaultBufferSize ()
Returns a default value for Publisher or Subscriber buffering, that may be used in the absence of other constraints.
final var size = Flow.defaultBufferSize();
System.out.println(size); // 256