本文介绍了订阅者可以充当发布者吗?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

就反应式流而言,有一个发布者,它可以有尽可能多的订阅者.

In terms of Reactive Streams, there is a Publisher and it could have as many Subscribers.

但是,假设订阅者从发布者那里收到一条消息.现在,此订户(例如Subs1)更改/修改了该消息,并将其传递给其他订户(例如Subs2),后者使用了已修改的消息.

But suppose, a subscriber gets a message from Publisher. Now this Subscriber(say Subs1) changes/modifies the message and passes it to some other Subscriber(say Subs2), which consumes the modified message.

那么,这个Subs1订阅者可以充当发布者,该发布者可以将消息传递给新的Subs2订阅者吗?

So can this Subs1 subscriber can act as a Publisher which can pass on message to new Subs2 subscriber?

我不确定是否可以,但是我认为这种情况是可能的.

I am not sure if it possible or not, but the scenario is possible i think.

如果可能,请提出一个可行的方法.

If its possible, please suggest a possible way to do this.

推荐答案

这是完成此操作的完整实现:​​

Here is the complete implementation to do this:

  1. 创建一个MyTransformer类,该类实现Processor并扩展SubmissionPublisher,因为它将同时充当Subscriber和Publisher:

  1. Create a MyTransformer class which implements Processor and extends SubmissionPublisher, as it will act both as Subscriber and Publisher:

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);
}



}

  • 创建一个TestSubscriber类,该类实现Subscriber接口并实现所需的方法:

  • Create an TestSubscriber class which implements the Subscriber interface and implement the required methods:

    在处理开始之前调用onSubscribe()方法.订阅的实例作为参数传递.这是一个类,用于控制订阅服务器和发布服务器之间的消息流.

    The onSubscribe() method is called before processing starts. The instance of the Subscription is passed as the argument. It is a class that is used to control the flow of messages between Subscriber and the Publisher.

    这里的主要方法是onNext()-每当发布者发布新消息时都会调用此方法.

    The main method here is onNext() – this is called whenever the Publisher publishes a new message.

    我们正在使用实现Publisher接口的SubmissionPublisher类.

    We are using the SubmissionPublisher class which implements the Publisher interface.

    我们将向发布者提交N个元素-我们的TestSubscriber将接收该元素.

    We’re going to be submitting N elements to the Publisher – which our TestSubscriber will be receiving.

    请注意,我们正在TestSubscriber实例上调用close()方法.它将在给定发布者的每个订阅者下面调用onComplete()回调.

    Note, that we’re calling the close() method on the instance of the TestSubscriber. It will invoke onComplete() callback underneath on every Subscriber of the given Publisher.

    import java.util.LinkedList;
    import java.util.List;
    import java.util.concurrent.Flow.Subscriber;
    import java.util.concurrent.Flow.Subscription;
    
    public class TestSubscriber<T> implements Subscriber<T> {
    
        private Subscription subscription;
    
        public List<T> consumed = new LinkedList<>();
    
        @Override
        public void onComplete() {
            System.out.println("Subsciber Completed");
        }
    
        @Override
        public void onError(Throwable arg0) {
            arg0.printStackTrace();
        }
    
        @Override
        public void onNext(T item) {
            System.out.println("In Subscriber Got : "+item);
            subscription.request(1);
    
        }
    
        @Override
        public void onSubscribe(Subscription subscription) {
            this.subscription = subscription;
            subscription.request(1);
        }
    
    }
    
    1. 这里是发布者正在发布String元素的处理流程.

    MyTransformer正在将String解析为Integer,这意味着此处需要进行转换.

    MyTransformer is parsing the String as Integer – which means a conversion needs to happening here.

    import java.util.List;
    import java.util.concurrent.SubmissionPublisher;;
    
    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();
    
        }
    }
    

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  • 07-12 17:58