在Spring-Integration-Kafka中使用@Gateway

Question

Using Spring-Integration-Kafka can we still use @MessagingGateway and @Gateway.

My current code looks like this:

@MessagingGateway
public interface OrderGateway {
 @Gateway(requestChannel = "requestChannel", replyChannel = "replyChannel",headers = {@GatewayHeader(name = "kafka_topic", value ="requestTopic"))
  Order order(Item item)
}

on my Spring Spring configuration:

@Bean
@ServiceActivator(inputChannel = "requestChannel")
public MessageHandler kafkaMessageHandler(KafkaTemplate kafkaTemplate) {
    KafkaProducerMessageHandler<String, String> messageHandler = new KafkaProducerMessageHandler<>(kafkaTemplate);
    messageHandler.setMessageKeyExpression(new LiteralExpression("spring-integration-kafka"));
    messageHandler.setTopicExpression(new SpelExpressionParser().parseExpression("headers.kafka_topic"));
    return messageHandler;
}

with this setup I get and error saying:

by: org.springframework.messaging.core.DestinationResolutionException: no output-channel or replyChannel header available  

Answer 1

You don't appear to have shown the complete configuration.

The gateway is expecting a reply but the kafkaMessageHandler produces no reply (unless the template is a ReplyingKafkaTemplate ) and will lose the replyChannel header.

So, presumably, you are trying to send a reply from someplace else.

If you are expecting request/reply semantics; use the new outbound gateway .

Where the template has to be a ReplyingKafkaTemplate .