Question

我有一个用Flink（Scala）编写的流WordCount示例示例。在其中，我想使用Flink-Kafka生产者将结果放入Kafka。但是它没有按预期工作。

我的代码如下：

object WordCount {
  def main(args: Array[String]) {
    // set up the execution environment
    val env = StreamExecutionEnvironment
      .getExecutionEnvironment
      .setStateBackend(new RocksDBStateBackend("file:///path/to/checkpoint", true))

    // start a checkpoint every 1000 ms
    env.enableCheckpointing(1000)

    // set mode to exactly-once (this is the default)
    env.getCheckpointConfig.setCheckpointingMode(CheckpointingMode.EXACTLY_ONCE)

    // make sure 500 ms of progress happen between checkpoints
    env.getCheckpointConfig.setMinPauseBetweenCheckpoints(500)

    // checkpoints have to complete within one minute, or are discarded
    env.getCheckpointConfig.setCheckpointTimeout(60000)

    // prevent the tasks from failing if an error happens in their checkpointing, the checkpoint will just be declined.
    env.getCheckpointConfig.setFailOnCheckpointingErrors(false)

    // allow only one checkpoint to be in progress at the same time
    env.getCheckpointConfig.setMaxConcurrentCheckpoints(1)

    // prepare Kafka consumer properties
    val kafkaConsumerProperties = new Properties
    kafkaConsumerProperties.setProperty("zookeeper.connect", "localhost:2181")
    kafkaConsumerProperties.setProperty("group.id", "flink")
    kafkaConsumerProperties.setProperty("bootstrap.servers", "localhost:9092")

    // set up Kafka Consumer
    val kafkaConsumer = new FlinkKafkaConsumer[String]("input", new SimpleStringSchema, kafkaConsumerProperties)

    println("Executing WordCount example.")

    // get text from Kafka
    val text = env.addSource(kafkaConsumer)

    val counts: DataStream[(String, Int)] = text
      // split up the lines in pairs (2-tuples) containing: (word,1)
      .flatMap(_.toLowerCase.split("\\W+"))
      .filter(_.nonEmpty)
      .map((_, 1))
      // group by the tuple field "0" and sum up tuple field "1"
      .keyBy(0)
      .mapWithState((in: (String, Int), count: Option[Int]) =>
        count match {
          case Some(c) => ((in._1, c), Some(c + in._2))
          case None => ((in._1, 1), Some(in._2 + 1))
        })

    // emit result
    println("Printing result to stdout.")
    counts.map(_.toString()).addSink(new FlinkKafkaProducer[String]("output", new SimpleStringSchema,
      kafkaProperties))

    // execute program
    env.execute("Streaming WordCount")
  }
}

我发送给Kafka input主题的数据是：

hi
hello

我在Kafka主题output中没有任何输出。由于我是Apache Flink的新手，所以我不知道如何获得预期的结果。谁能帮助我实现正确的行为？

Answer 1

我将您的代码运行到本地环境中，一切正常。我认为您可以尝试以下命令：

./kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic  output --from-beginning

Apache Flink：IDE执行中的Kafka Producer无法正常工作

1 个答案: