異常：org.springframework.messaging.MessageDeliveryException：Dispatcher 沒有頻道訂閱者

Question

我有一個用於探索 Spring Cloud Stream 中新增功能的沙箱，但是我在一個 Spring Cloud Stream 應用程序中使用 Function 和 Supplier 時遇到了問題。

在代碼中，我使用了docs 中描述的示例。

首先，我在application.yml添加了具有相應spring.cloud.stream.bindings和spring.cloud.stream.function.definition屬性的項目Function<String, String> 。 一切正常，我將消息發布到my-fun-in Kafka 主題，應用程序執行功能並將結果發送到my-fun-out主題。

然后我將Supplier<Flux<String>>到具有相應spring.cloud.stream.bindings的同一個項目中，並將spring.cloud.stream.function.definition值更新為fun;sup 。 在這里，奇怪的事情開始發生。 當我嘗試啟動應用程序時，我收到以下錯誤：

2020-01-15 01:45:16.608 ERROR 10128 --- [oundedElastic-1] o.s.integration.handler.LoggingHandler   : org.springframework.messaging.MessageDeliveryException: Dispatcher has no subscribers for channel 'application.sup-out-0'.; nested exception is org.springframework.integration.MessageDispatchingException: Dispatcher has no subscribers, failedMessage=GenericMessage [payload=byte[20], headers={contentType=application/json, id=89301e00-b285-56e0-cb4d-8133555c8905, timestamp=1579045516603}], failedMessage=GenericMessage [payload=byte[20], headers={contentType=application/json, id=89301e00-b285-56e0-cb4d-8133555c8905, timestamp=1579045516603}]
    at org.springframework.integration.channel.AbstractSubscribableChannel.doSend(AbstractSubscribableChannel.java:77)
    at org.springframework.integration.channel.AbstractMessageChannel.send(AbstractMessageChannel.java:453)
    at org.springframework.integration.channel.AbstractMessageChannel.send(AbstractMessageChannel.java:403)
    at org.springframework.messaging.core.GenericMessagingTemplate.doSend(GenericMessagingTemplate.java:187)
    at org.springframework.messaging.core.GenericMessagingTemplate.doSend(GenericMessagingTemplate.java:166)
    at org.springframework.messaging.core.GenericMessagingTemplate.doSend(GenericMessagingTemplate.java:47)
    at org.springframework.messaging.core.AbstractMessageSendingTemplate.send(AbstractMessageSendingTemplate.java:109)
    at org.springframework.integration.router.AbstractMessageRouter.doSend(AbstractMessageRouter.java:206)
    at org.springframework.integration.router.AbstractMessageRouter.handleMessageInternal(AbstractMessageRouter.java:188)
    at org.springframework.integration.handler.AbstractMessageHandler.handleMessage(AbstractMessageHandler.java:170)
    at org.springframework.integration.handler.AbstractMessageHandler.onNext(AbstractMessageHandler.java:219)
    at org.springframework.integration.handler.AbstractMessageHandler.onNext(AbstractMessageHandler.java:57)
    at org.springframework.integration.endpoint.ReactiveStreamsConsumer$DelegatingSubscriber.hookOnNext(ReactiveStreamsConsumer.java:165)
    at org.springframework.integration.endpoint.ReactiveStreamsConsumer$DelegatingSubscriber.hookOnNext(ReactiveStreamsConsumer.java:148)
    at reactor.core.publisher.BaseSubscriber.onNext(BaseSubscriber.java:160)
    at reactor.core.publisher.FluxDoFinally$DoFinallySubscriber.onNext(FluxDoFinally.java:123)
    at reactor.core.publisher.EmitterProcessor.drain(EmitterProcessor.java:426)
    at reactor.core.publisher.EmitterProcessor.onNext(EmitterProcessor.java:268)
    at reactor.core.publisher.FluxCreate$BufferAsyncSink.drain(FluxCreate.java:793)
    at reactor.core.publisher.FluxCreate$BufferAsyncSink.next(FluxCreate.java:718)
    at reactor.core.publisher.FluxCreate$SerializedSink.next(FluxCreate.java:153)
    at org.springframework.integration.channel.FluxMessageChannel.doSend(FluxMessageChannel.java:63)
    at org.springframework.integration.channel.AbstractMessageChannel.send(AbstractMessageChannel.java:453)
    at org.springframework.integration.channel.AbstractMessageChannel.send(AbstractMessageChannel.java:403)
    at org.springframework.integration.channel.FluxMessageChannel.lambda$subscribeTo$2(FluxMessageChannel.java:83)
    at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onNext(FluxPeekFuseable.java:189)
    at reactor.core.publisher.FluxPublishOn$PublishOnSubscriber.runAsync(FluxPublishOn.java:398)
    at reactor.core.publisher.FluxPublishOn$PublishOnSubscriber.run(FluxPublishOn.java:484)
    at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:84)
    at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:37)
    at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
    at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: org.springframework.integration.MessageDispatchingException: Dispatcher has no subscribers, failedMessage=GenericMessage [payload=byte[20], headers={contentType=application/json, id=89301e00-b285-56e0-cb4d-8133555c8905, timestamp=1579045516603}]
    at org.springframework.integration.dispatcher.UnicastingDispatcher.doDispatch(UnicastingDispatcher.java:139)
    at org.springframework.integration.dispatcher.UnicastingDispatcher.dispatch(UnicastingDispatcher.java:106)
    at org.springframework.integration.channel.AbstractSubscribableChannel.doSend(AbstractSubscribableChannel.java:73)
    ... 34 more

之后我嘗試了幾件事：

1. 將spring.cloud.stream.function.definition為fun （禁用與外部目標的sup bean 綁定）。 應用程序啟動，功能工作，供應商不工作。 一切都如預期。
2. 將spring.cloud.stream.function.definition更改為sup （禁用fun bean 綁定到外部目標）。 應用程序啟動，功能不起作用，供應商工作（每秒向my-sup-out主題生成消息）。 一切都和預期的一樣。
3. 將spring.cloud.stream.function.definition值更新為fun;sup 。 應用程序沒有啟動，得到相同的 MessageDeliveryException。
4. 將spring.cloud.stream.function.definition值交換為sup;fun 。 應用程序啟動，供應商工作，但功能不起作用（沒有向my-fun-out主題發送消息）。

最后一個比錯誤更讓我困惑）所以現在我需要有人的幫助來解決問題。

我錯過了什么配置嗎？ 為什么要更改以;分隔的 bean 順序; 在spring.cloud.stream.function.definition導致不同的結果？

完整的項目上傳到GitHub並添加到下面：

流應用程序.java：

package com.kaine;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import reactor.core.publisher.Flux;

import java.util.function.Function;
import java.util.function.Supplier;

@SpringBootApplication
public class StreamApplication {

    public static void main(String[] args) {
        SpringApplication.run(StreamApplication.class);
    }

    @Bean
    public Function<String, String> fun() {
        return value -> value.toUpperCase();
    }

    @Bean
    public Supplier<Flux<String>> sup() {
        return () -> Flux.from(emitter -> {
            while (true) {
                try {
                    emitter.onNext("Hello from Supplier!");
                    Thread.sleep(1000);
                } catch (Exception e) {
                    // ignore
                }
            }
        });
    }
}

應用程序.yml

spring:
  cloud:
    stream:
      function:
        definition: fun;sup
      bindings:
        fun-in-0:
          destination: my-fun-in
        fun-out-0:
          destination: my-fun-out
        sup-out-0:
          destination: my-sup-out

build.gradle.kts：

plugins {
    java
}

group = "com.kaine"
version = "1.0-SNAPSHOT"

repositories {
    mavenCentral()
}

dependencies {
        implementation(platform("org.springframework.cloud:spring-cloud-dependencies:Hoxton.SR1"))
        implementation("org.springframework.cloud:spring-cloud-starter-stream-kafka")

        implementation(platform("org.springframework.boot:spring-boot-dependencies:2.2.2.RELEASE"))
}

configure<JavaPluginConvention> {
    sourceCompatibility = JavaVersion.VERSION_11
}

Answer 1

實際上，這是我們文檔的一個問題，因為我相信我們為他的案例提供了一個反應性供應商的壞例子。 問題是您的供應商處於無限阻塞循環中。 它基本上永遠不會回來。 因此，請將其更改為：

@Bean
public Supplier<Flux<String>> sup() {
    return () -> Flux.fromStream(Stream.generate(new Supplier<String>() {

        @Override
        public String get() {
            try {
                Thread.sleep(1000);
                return "Hello from Supplier";
            } catch (Exception e) {
                // ignore
            }
        }

    })).subscribeOn(Schedulers.elastic()).share();
}