reactive-programming - 如何将消息传递给另一个订阅者？

Question

我正在学习 Java 9 的 Reactive Stream API。

因为它有发布者和订阅者，订阅者订阅发布者，订阅者也实现了以下消息：

public class TestSubscriber<T> implements Subscriber<T> {

    @Override
    public void onComplete() {
        // TODO Auto-generated method stub

    }

    @Override
    public void onError(Throwable arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onNext(T arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onSubscribe(Subscription arg0) {
        // TODO Auto-generated method stub

    }

}

我没有在订阅者中找到任何将消息传递/传输给另一个订阅者的方法。有什么建议么？

Answer 1

这可以通过实现 Flow.Processor 来完成，如下所示：

import java.util.concurrent.Flow;
import java.util.concurrent.Flow.Subscription;
import java.util.concurrent.SubmissionPublisher;
import java.util.function.Function;

public class MyTransformer<T, R> extends SubmissionPublisher<R> implements Flow.Processor<T, R> {

    private Function<T, R> function;
    private Flow.Subscription subscription;

    public MyTransformer(Function<T, R> function) {
        super();
        this.function = function;
    }

    @Override
    public void onComplete() {
        System.out.println("Transformer Completed");
    }

    @Override
    public void onError(Throwable e) {
        e.printStackTrace();
    }

    @Override
    public void onNext(T item) {
        System.out.println("Transformer Got : "+item);
        submit(function.apply(item));
        subscription.request(1);

    }

    @Override
    public void onSubscribe(Subscription subscription) {
        this.subscription = subscription;
        subscription.request(1);
    }


}

并且在调用它时使用如下：

public class TestTransformer {

    public static void main(String... args) {
        SubmissionPublisher<String> publisher = new SubmissionPublisher<>();
        MyTransformer<String, Integer> transformProcessor = new MyTransformer<>(Integer::parseInt);

        TestSubscriber<Integer> subscriber = new TestSubscriber<>();
        List<String> items = List.of("1", "2", "3");

        List<Integer> expectedResult = List.of(1, 2, 3);

        publisher.subscribe(transformProcessor);
        transformProcessor.subscribe(subscriber);
        items.forEach(publisher::submit);
        publisher.close();

    }
}