Question

我开发了异步Spring Cloud Stream服务，我正在尝试开发一种边缘服务，该服务使用@MessagingGateway来提供对异步服务的同步访问。

我目前正在获得以下堆栈跟踪：

Caused by: org.springframework.messaging.core.DestinationResolutionException: no output-channel or replyChannel header available
at org.springframework.integration.handler.AbstractMessageProducingHandler.sendOutput(AbstractMessageProducingHandler.java:355)
at org.springframework.integration.handler.AbstractMessageProducingHandler.produceOutput(AbstractMessageProducingHandler.java:271)
at org.springframework.integration.handler.AbstractMessageProducingHandler.sendOutputs(AbstractMessageProducingHandler.java:188)
at org.springframework.integration.handler.AbstractReplyProducingMessageHandler.handleMessageInternal(AbstractReplyProducingMessageHandler.java:115)
at org.springframework.integration.handler.AbstractMessageHandler.handleMessage(AbstractMessageHandler.java:127)
at org.springframework.integration.dispatcher.AbstractDispatcher.tryOptimizedDispatch(AbstractDispatcher.java:116)
... 47 common frames omitted

我的@MessagingGateway：

@EnableBinding(AccountChannels.class)
@MessagingGateway

public interface AccountService {
  @Gateway(requestChannel = AccountChannels.CREATE_ACCOUNT_REQUEST,replyChannel = AccountChannels.ACCOUNT_CREATED, replyTimeout = 60000, requestTimeout = 60000)
  Account createAccount(@Payload Account account, @Header("Authorization") String authorization);
}

如果我通过@StreamListener在回复频道上使用该消息，它可以正常工作：

  @HystrixCommand(commandKey = "acounts-edge:accountCreated", fallbackMethod = "accountCreatedFallback", commandProperties = {@HystrixProperty(name = "execution.isolation.strategy", value = "SEMAPHORE")}, ignoreExceptions = {ClientException.class})
  @StreamListener(AccountChannels.ACCOUNT_CREATED)
  public void accountCreated(Account account, @Header(name = "spanTraceId", required = false) String traceId) {
    try {
      if (log.isInfoEnabled()) {
        log.info(new StringBuilder("Account created: ").append(objectMapper.writeValueAsString(account)).toString());
      }
    } catch (JsonProcessingException e) {
      log.error(e.getMessage(), e);
    }
  }

在生产者方面，我正在配置requiredGroups以确保多个消费者可以处理消息，相应地，消费者具有匹配的group配置。

消费者：

spring:
  cloud:
    stream:
      bindings:
        create-account-request:
          binder: rabbit1
          contentType: application/json
          destination: create-account-request
          requiredGroups: accounts-service-create-account-request
        account-created:
          binder: rabbit1
          contentType: application/json
          destination: account-created
          group: accounts-edge-account-created

制片：

spring:
  cloud:
    stream:
      bindings:
        create-account-request:
          binder: rabbit1
          contentType: application/json
          destination: create-account-request
          group: accounts-service-create-account-request
        account-created:
          binder: rabbit1
          contentType: application/json
          destination: account-created
          requiredGroups: accounts-edge-account-created

生产者端处理请求并发送响应的代码：

  accountChannels.accountCreated().send(MessageBuilder.withPayload(accountService.createAccount(account)).build());

我可以调试并看到请求已被接收和处理，但是当响应被发送到回复通道时，就会发生错误。

为了让@MessagingGateway正常工作，我缺少哪些配置和/或代码？我知道我正在将Spring Integration和Spring Cloud Gateway结合起来，所以我不确定是否一起使用它们会导致问题。

Answer 1

这是一个很好的问题，也是一个好主意。但它不会那么容易。

首先，我们必须自己确定gateway表示request/reply，因此correlation。这可以@MessagingGateway通过replyChannel标题面向TemporaryReplyChannel实例提供。即使您有明确的replyChannel = AccountChannels.ACCOUNT_CREATED，也只能通过提到的标头及其值进行关联。事实上，TemporaryReplyChannel不可序列化，无法通过网络传输到另一方的消费者。

幸运的是，Spring Integration为我们提供了一些解决方案。它是HeaderEnricher背后的headerChannelsToString及其HeaderChannelRegistry选项的一部分：

从Spring Integration 3.0开始，可以使用新的子元素;它没有属性。这会将现有的replyChannel和errorChannel标头（当它们是MessageChannel时）转换为String，并将通道存储在注册表中，以便在发送回复或处理错误时进行解决。这对于标题可能丢失的情况很有用;例如，将消息序列化到消息存储库或通过JMS传输消息时。如果标头尚不存在，或者它不是MessageChannel，则不会进行任何更改。

https://docs.spring.io/spring-integration/docs/5.0.0.RELEASE/reference/html/messaging-transformation-chapter.html#header-enricher

但在这种情况下，您必须从网关引入一个内部频道到HeaderEnricher，只有最后一个频道会将消息发送到AccountChannels.CREATE_ACCOUNT_REQUEST。因此，replyChannel标头将转换为字符串表示，并能够通过网络传输。在发送回复时，在消费者方面，您应该确保转移replyChannel标题，就像它一样。因此，当消息将到达生产者端的AccountChannels.ACCOUNT_CREATED时，我们有@MessagingGateway，相关机制能够将信道标识符转换为正确的TemporaryReplyChannel并关联回复等待的网关电话。

此处只有您的生产者应用程序必须作为AccountChannels.ACCOUNT_CREATED组中的单个使用者的问题 - 我们必须确保云中只有一个实例一次运行。仅仅因为只有一个实例在其内存中有TemporaryReplyChannel。

有关网关的更多信息：https://docs.spring.io/spring-integration/docs/5.0.0.RELEASE/reference/html/messaging-endpoints-chapter.html#gateway

<强>更新

一些帮助代码：

@EnableBinding(AccountChannels.class)
@MessagingGateway

public interface AccountService {
  @Gateway(requestChannel = AccountChannels.INTERNAL_CREATE_ACCOUNT_REQUEST, replyChannel = AccountChannels.ACCOUNT_CREATED, replyTimeout = 60000, requestTimeout = 60000)
  Account createAccount(@Payload Account account, @Header("Authorization") String authorization);
}

@Bean
public IntegrationFlow headerEnricherFlow() {
   return IntegrationFlows.from(AccountChannels.INTERNAL_CREATE_ACCOUNT_REQUEST)
            .enrichHeaders(headerEnricher -> headerEnricher.headerChannelsToString())
            .channel(AccountChannels.CREATE_ACCOUNT_REQUEST)
            .get();

}

<强>更新

一些简单的应用程序来演示PoC：

@EnableBinding({ Processor.class, CloudStreamGatewayApplication.GatewayChannels.class })
@SpringBootApplication
public class CloudStreamGatewayApplication {

    interface GatewayChannels {

        String REQUEST = "request";

        @Output(REQUEST)
        MessageChannel request();


        String REPLY = "reply";

        @Input(REPLY)
        SubscribableChannel reply();
    }

    private static final String ENRICH = "enrich";


    @MessagingGateway
    public interface StreamGateway {

        @Gateway(requestChannel = ENRICH, replyChannel = GatewayChannels.REPLY)
        String process(String payload);

    }

    @Bean
    public IntegrationFlow headerEnricherFlow() {
        return IntegrationFlows.from(ENRICH)
                .enrichHeaders(HeaderEnricherSpec::headerChannelsToString)
                .channel(GatewayChannels.REQUEST)
                .get();
    }

    @StreamListener(Processor.INPUT)
    @SendTo(Processor.OUTPUT)
    public Message<?> process(Message<String> request) {
        return MessageBuilder.withPayload(request.getPayload().toUpperCase())
                .copyHeaders(request.getHeaders())
                .build();
    }


    public static void main(String[] args) {
        ConfigurableApplicationContext applicationContext =
                SpringApplication.run(CloudStreamGatewayApplication.class, args);

        StreamGateway gateway = applicationContext.getBean(StreamGateway.class);

        String result = gateway.process("foo");

        System.out.println(result);
    }

}

application.yml：

spring:
  cloud:
    stream:
      bindings:
        input:
          destination: requests
        output:
          destination: replies
        request:
          destination: requests
        reply:
          destination: replies

我使用spring-cloud-starter-stream-rabbit。

MessageBuilder.withPayload(request.getPayload().toUpperCase())
            .copyHeaders(request.getHeaders())
            .build()

技巧是否将请求标头复制到回复消息。因此，网关能够在回复端将报头中的信道标识符转换为适当的TemporaryReplyChannel，以便将回复正确地传送给网关的呼叫者。

关于此问题的SCST问题：https://github.com/spring-cloud/spring-cloud-stream/issues/815

Answer 2

在Artem的帮助下，我找到了我想要的解决方案。我已经发布了Artem发布的代码并将其拆分为两个服务，即Gateway服务和CloudStream服务。我还添加了@RestController用于测试目的。这基本上模仿了我想用持久队列做的事情。感谢Artem的帮助！我非常感谢你的时间！我希望这有助于其他想要做同样事情的人。

网关代码

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.stream.annotation.EnableBinding;
import org.springframework.cloud.stream.annotation.Input;
import org.springframework.cloud.stream.annotation.Output;

import org.springframework.context.annotation.Bean;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.integration.annotation.Gateway;
import org.springframework.integration.annotation.MessagingGateway;
import org.springframework.integration.dsl.HeaderEnricherSpec;
import org.springframework.integration.dsl.IntegrationFlow;
import org.springframework.integration.dsl.IntegrationFlows;
import org.springframework.messaging.MessageChannel;
import org.springframework.messaging.SubscribableChannel;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@EnableBinding({GatewayApplication.GatewayChannels.class})
@SpringBootApplication
public class GatewayApplication {

  interface GatewayChannels {

    String TO_UPPERCASE_REPLY = "to-uppercase-reply";
    String TO_UPPERCASE_REQUEST = "to-uppercase-request";

    @Input(TO_UPPERCASE_REPLY)
    SubscribableChannel toUppercaseReply();

    @Output(TO_UPPERCASE_REQUEST)
    MessageChannel toUppercaseRequest();
  }

  @MessagingGateway
  public interface StreamGateway {
    @Gateway(requestChannel = ENRICH, replyChannel = GatewayChannels.TO_UPPERCASE_REPLY)
    String process(String payload);
  }

  private static final String ENRICH = "enrich";

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

  @Bean
  public IntegrationFlow headerEnricherFlow() {
    return IntegrationFlows.from(ENRICH).enrichHeaders(HeaderEnricherSpec::headerChannelsToString)
        .channel(GatewayChannels.TO_UPPERCASE_REQUEST).get();
  }

  @RestController
  public class UppercaseController {
    @Autowired
    StreamGateway gateway;

    @GetMapping(value = "/string/{string}",
        produces = {MediaType.APPLICATION_JSON_VALUE, MediaType.APPLICATION_XML_VALUE})
    public ResponseEntity<String> getUser(@PathVariable("string") String string) {
      return new ResponseEntity<String>(gateway.process(string), HttpStatus.OK);
    }
  }

}

网关配置（application.yml）

spring:
  cloud:
    stream:
      bindings:
        to-uppercase-request:
          destination: to-uppercase-request
          producer:
            required-groups: stream-to-uppercase-request
        to-uppercase-reply:
          destination: to-uppercase-reply
          group: gateway-to-uppercase-reply
server:
  port: 8080

CloudStream代码

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.stream.annotation.EnableBinding;
import org.springframework.cloud.stream.annotation.Input;
import org.springframework.cloud.stream.annotation.Output;
import org.springframework.cloud.stream.annotation.StreamListener;
import org.springframework.messaging.Message;
import org.springframework.messaging.MessageChannel;
import org.springframework.messaging.SubscribableChannel;
import org.springframework.messaging.handler.annotation.SendTo;
import org.springframework.messaging.support.MessageBuilder;

@EnableBinding({CloudStreamApplication.CloudStreamChannels.class})
@SpringBootApplication
public class CloudStreamApplication {

  interface CloudStreamChannels {

    String TO_UPPERCASE_REPLY = "to-uppercase-reply";
    String TO_UPPERCASE_REQUEST = "to-uppercase-request";

    @Output(TO_UPPERCASE_REPLY)
    SubscribableChannel toUppercaseReply();

    @Input(TO_UPPERCASE_REQUEST)
    MessageChannel toUppercaseRequest();
  }

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

  @StreamListener(CloudStreamChannels.TO_UPPERCASE_REQUEST)
  @SendTo(CloudStreamChannels.TO_UPPERCASE_REPLY)
  public Message<?> process(Message<String> request) {
    return MessageBuilder.withPayload(request.getPayload().toUpperCase())
        .copyHeaders(request.getHeaders()).build();
  }

}

CloudStream Config（application.yml）

spring:
  cloud:
    stream:
      bindings:
        to-uppercase-request:
          destination: to-uppercase-request
          group: stream-to-uppercase-request
        to-uppercase-reply:
          destination: to-uppercase-reply
          producer:
            required-groups: gateway-to-uppercase-reply
server:
  port: 8081

Answer 3

嗯，我和你想要完成的事情有点混淆，但如果我们能弄清楚这一点，那就说吧。混合SI和SCSt绝对是自然的，因为一个建立在另一个所以应该工作：这是一个示例代码片段，我刚刚从一个旧样本中挖掘出来，它暴露了REST端点，然后委托（通过Gateway）到Source的输出通道。看看是否有帮助：

@EnableBinding(Source.class)
@SpringBootApplication
@RestController
public class FooApplication {
    . . . 

    @Autowired
    private Source channels;

    @Autowired
    private CompletionService completionService;

    @RequestMapping("/complete")
    public String completeRequest(@RequestParam int id) {
        this.completionService.complete("foo");
        return "OK";
    }

    @MessagingGateway
    interface CompletionService {
        @Gateway(requestChannel = Source.OUTPUT)
        void complete(String message);
    }
}

如何使用Spring Cloud Stream MessageChannels配置@MessagingGateway？

3 个答案: