我正在尝试创建一个简单的生产者，它用配置提供的一些分区创建一个主题。
根据阿尔帕卡制作人的说法 org.apache.kafka.clients.producer.ProducerConfig 可以设置为 kafka-clients 部分。而且，还有一个 num.partitions producer api doc中注解的属性。
因此，我把这个属性添加到我的 application.conf 文件如下：

topic = "topic"
topic = ${?TOPIC}

# Properties for akka.kafka.ProducerSettings can be

# defined in this section or a configuration section with

# the same layout.

akka.kafka.producer {
  # Tuning parameter of how many sends that can run in parallel.
  parallelism = 100
  parallelism = ${?PARALLELISM}

  # Duration to wait for `KafkaConsumer.close` to finish.
  close-timeout = 20s

  # Fully qualified config path which holds the dispatcher configuration
  # to be used by the producer stages. Some blocking may occur.
  # When this value is empty, the dispatcher configured for the stream
  # will be used.
  use-dispatcher = "akka.kafka.default-dispatcher"

  # The time interval to commit a transaction when using the `Transactional.sink` or `Transactional.flow`
  eos-commit-interval = 100ms

  # Properties defined by org.apache.kafka.clients.producer.ProducerConfig
  # can be defined in this configuration section.
  kafka-clients {
    bootstrap.servers = "my-kafka:9092"
    bootstrap.servers = ${?BOOTSTRAPSERVERS}
    num.partitions = "3"
    num.partitions = ${?NUM_PARTITIONS}
  }
}

生产商申请代码如下：

object Main extends App {

  val config = ConfigFactory.load()

  implicit val system: ActorSystem = ActorSystem("producer")
  implicit val materializer: Materializer = ActorMaterializer()

  val producerConfigs = config.getConfig("akka.kafka.producer")
  val producerSettings = ProducerSettings(producerConfigs, new StringSerializer, new StringSerializer)

  val topic = config.getString("topic")

  val done: Future[Done] =
    Source(1 to 100000)
      .map(_.toString)
      .map(value => new ProducerRecord[String, String](topic, value))
      .runWith(Producer.plainSink(producerSettings))

  implicit val ec: ExecutionContextExecutor = system.dispatcher
  done onComplete  {
    case Success(_) => println("Done"); system.terminate()
    case Failure(err) => println(err.toString); system.terminate()
  }

}

但是，这不管用。producer使用单个分区创建主题，而不是使用配置设置的3个分区：

num.partitions = "3"

最后，kafkacat输出如下：

~$ kafkacat -b my-kafka:9092 -L
Metadata for all topics (from broker -1: my-kafka:9092/bootstrap):
 3 brokers:
  broker 2 at my-kafka-2.my-kafka-headless.default:9092
  broker 1 at my-kafka-1.my-kafka-headless.default:9092
  broker 0 at my-kafka-0.my-kafka-headless.default:9092
 1 topics:
  topic "topic" with 1 partitions:
    partition 0, leader 2, replicas: 2, isrs: 2

怎么了？是否可以在中设置kafka producer api的属性 kafka-clients 使用alpakka的部分？