kafka 的 createDirectStream

kafka api中给出2类直接获取流的接口：createStream和createDirectStream。

createStream比较简单，只需topic、groupid、zookeeper就可以直接获取流，brokers和offset都是黑盒无需进行控制，但在项目中往往不受控。以下是部分源码：

/**
   * Create an input stream that pulls messages from Kafka Brokers.
   * @param ssc       StreamingContext object
   * @param zkQuorum  Zookeeper quorum (hostname:port,hostname:port,..)
   * @param groupId   The group id for this consumer
   * @param topics    Map of (topic_name -> numPartitions) to consume. Each partition is consumed
   *                  in its own thread
   * @param storageLevel  Storage level to use for storing the received objects
   *                      (default: StorageLevel.MEMORY_AND_DISK_SER_2)
   * @return DStream of (Kafka message key, Kafka message value)
   */
  def createStream(
      ssc: StreamingContext,
      zkQuorum: String,
      groupId: String,
      topics: Map[String, Int],
      storageLevel: StorageLevel = StorageLevel.MEMORY_AND_DISK_SER_2
    ): ReceiverInputDStream[(String, String)] = {
    val kafkaParams = Map[String, String](
      "zookeeper.connect" -> zkQuorum, "group.id" -> groupId,
      "zookeeper.connection.timeout.ms" -> "10000")
    createStream[String, String, StringDecoder, StringDecoder](
      ssc, kafkaParams, topics, storageLevel)
  }

KafkaUtils.createStream