java.lang.NullPointerException：使用 Avro 格式的 Spring Cloud Stream 3 Kafka Function Producer 中的 null

Question

I'm upgrading an existing Spring Cloud Stream application to use the new Spring Cloud Function producers. The generated messages use Avro format.

This is my whole setup:

spring:
  cloud:
    stream:
      schema-registry-client:
        endpoint: ${schema-registry.url:http://localhost:8081}
      bindings:
        info-out-0:
          destination: info
          producer:
            useNativeEncoding: true
          contentType: application/*+avro
      kafka:
        binder:
          brokers: ${kafka.brokers:localhost}
          transaction:
            transaction-id-prefix: info-tx-
            producer:
              configuration:
                retries: 2
                acks: all
                key:
                  serializer: io.confluent.kafka.serializers.KafkaAvroSerializer
                  subject:
                    name:
                      strategy: io.confluent.kafka.serializers.subject.RecordNameStrategy
                value:
                  serializer: io.confluent.kafka.serializers.KafkaAvroSerializer
                  subject:
                    name:
                      strategy: io.confluent.kafka.serializers.subject.RecordNameStrategy
                schema:
                  registry:
                    url: ${spring.cloud.stream.schema-registry-client.endpoint}
                useNativeEncoding: true
    function:
      definition: info
  kafka:
    bootstrap-servers: ${kafka.brokers:localhost:9092}

@Configuration
class SchemaRegistryConfiguration {

    @Bean
    fun schemaRegistryClient(@Value("\${spring.cloud.stream.schema-registry-client.endpoint}") endpoint: String): SchemaRegistryClient {
        val client = ConfluentSchemaRegistryClient()
        client.setEndpoint(endpoint)
        return client
    }
}

@Configuration
class KafkaProducerConfiguration {

    @Bean
    fun infoMonoProcessor(): MonoProcessor<Message<*>> {
        return MonoProcessor.create<Message<*>>()
    }

    @Bean
    fun info(): Supplier<Mono<Message<*>>> {
        return Supplier { infoMonoProcessor() }
    }

@Component
class InfoProducer(@Qualifier("infoMonoProcessor") private val infoProcessor: MonoProcessor<Message<*>>) {

    @Transactional
    fun send(info: Info): Mono<Unit> {
        return Mono.fromCallable {
                val infoReceived = InfoReceived(info)
                val message = MessageBuilder.withPayload(infoReceived)
                        .setHeader(KafkaHeaders.TIMESTAMP, dateTime)
                        .build()
                infoProcessor.onNext(message)
            }
        }.subscribeOn(Schedulers.elastic())
    }

}

There's a REST endpoint that receives some info and sends it to the output topic using the InfoProducer :

@RestController
@RequestMapping("/api/v1/info")
class InfoRestController(private val infoProducer: InfoProducer) {

    @PostMapping
    @ResponseStatus(CREATED)
    fun registerInfo(@RequestBody info: Info): Mono<Unit> {
        return infoProducer.send(info)
    }

The problem is I'm getting this ugly exception:

java.lang.NullPointerException: null
    at org.springframework.cloud.function.context.catalog.BeanFactoryAwareFunctionRegistry$FunctionInvocationWrapper.convertOutputValueIfNecessary(BeanFactoryAwareFunctionRegistry.java:601) ~[spring-cloud-function-context-3.0.0.RELEASE.jar:3.0.0.RELEASE]
    at org.springframework.cloud.function.context.catalog.BeanFactoryAwareFunctionRegistry$FunctionInvocationWrapper.lambda$convertOutputPublisherIfNecessary$4(BeanFactoryAwareFunctionRegistry.java:640) ~[spring-cloud-function-context-3.0.0.RELEASE.jar:3.0.0.RELEASE]
    at reactor.core.publisher.FluxMap$MapSubscriber.onNext(FluxMap.java:100) ~[reactor-core-3.3.0.RELEASE.jar:3.3.0.RELEASE]
    at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1592) ~[reactor-core-3.3.0.RELEASE.jar:3.3.0.RELEASE]
    at reactor.core.publisher.MonoProcessor.onNext(MonoProcessor.java:317) ~[reactor-core-3.3.0.RELEASE.jar:3.3.0.RELEASE]
    at xxx.InfoProducer$send$1.call(InfoProducer.kt:48) ~[classes/:na]
    at xxx.InfoProducer$send$1.call(InfoProducer.kt:25) ~[classes/:na]
    at reactor.core.publisher.MonoCallable.call(MonoCallable.java:91) ~[reactor-core-3.3.0.RELEASE.jar:3.3.0.RELEASE]
    at reactor.core.publisher.FluxSubscribeOnCallable$CallableSubscribeOnSubscription.run(FluxSubscribeOnCallable.java:225) ~[reactor-core-3.3.0.RELEASE.jar:3.3.0.RELEASE]
    at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:68) ~[reactor-core-3.3.0.RELEASE.jar:3.3.0.RELEASE]
    at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:28) ~[reactor-core-3.3.0.RELEASE.jar:3.3.0.RELEASE]
    at java.base/java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:264) ~[na:na]
    at java.base/java.util.concurrent.FutureTask.run(FutureTask.java) ~[na:na]
    at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304) ~[na:na]
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
    at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]

2019-12-11 16:41:43.985 DEBUG 22622 --- [      elastic-2] o.s.http.codec.json.Jackson2JsonEncoder  : [23177c31] Encoding [kotlin.Unit]

In BeanFactoryAwareFunctionRegistry acceptedOutputMimeTypes is an empty array.

What's the problem here?

Answer 1

Since you are using native encoding and the avro serializers provided by Confluent, I don't see the need for using Spring Cloud schema registry components here. You can remove SchemaRegistryConfiguration from your setup. You also don't need this:

spring:
  cloud:
    stream:
      schema-registry-client:
        endpoint: ${schema-registry.url:http://localhost:8081}

I suggest also not using ${spring.cloud.stream.schema-registry-client.endpoint} here, but use something more explicit.

schema:
                  registry:
                    url: http://localhost:8081

See this example .

If you are still having issues, could you share a reproducible sample?