MessageDeliveryException，在一个Spring Cloud Stream应用程序中使用Function和Supplier的情况。我错过了什么吗？

Question

我有一个沙箱，用于在Spring Cloud Stream中探索新添加的功能，但是在一个Spring Cloud Stream应用程序中使用Function和Supplier时遇到了问题。

在代码中，我使用了docs中描述的示例。

首先，我在Function<String, String>中添加了具有相应spring.cloud.stream.bindings和spring.cloud.stream.function.definition属性的项目application.yml。一切正常，我将消息发布到my-fun-in Kafka主题，应用程序执行功能并将结果发送到my-fun-out主题。

然后我将Supplier<Flux<String>>与相应的spring.cloud.stream.bindings添加到同一项目中，并将spring.cloud.stream.function.definition值更新为fun;sup。在这里，奇怪的事情开始发生。当我尝试启动应用程序时，出现以下错误：

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

在尝试了几件事之后：

1. 将spring.cloud.stream.function.definition还原为fun（禁用将sup bean绑定到外部目标）。应用程序启动，功能正常，供应商无效。一切都按预期。
2. 将spring.cloud.stream.function.definition更改为sup（禁用将fun bean绑定到外部目标）。应用程序启动，功能不起作用，供应商正常工作（每秒向my-sup-out主题产生一条消息）。一切也如预期。
3. 将spring.cloud.stream.function.definition值更新为fun;sup。应用程序未启动，出现相同的MessageDeliveryException。
4. 将spring.cloud.stream.function.definition值交换为sup;fun。应用程序已启动，供应商正常工作，但功能不起作用（未向my-fun-out主题发送消息）。

最后一个使我困惑的不只是错误，所以现在我需要别人的帮助来解决问题。

我是否错过了某项变形？为什么更改;中以spring.cloud.stream.function.definition分隔的bean顺序会导致不同的结果？

完整的项目已上传到GitHub，并在下面添加：

StreamApplication.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
                }
            }
        });
    }
}

application.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

实际上，这是我们文档的一个问题，因为我认为我们为他的案例提供了一个被动的供应商的不良示例。问题是您的供应商处于无限阻塞循环中。它基本上永远不会返回。因此，请将其更改为：

@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();
}