spark streaming updateStateByKey 用法

object NetworkWordCount {
  def main(args: Array[String]) {
    if (args.length < 2) {
      System.err.println("Usage: NetworkWordCount <hostname> <port>")
      System.exit(1)
    }


    val sparkConf = new SparkConf().setAppName("NetworkWordCount")
    val ssc = new StreamingContext(sparkConf, Seconds(10))
    //使用updateStateByKey前需要设置checkpoint
    ssc.checkpoint("hdfs://master:8020/spark/checkpoint")

    val addFunc = (currValues: Seq[Int], prevValueState: Option[Int]) => {
      //通过Spark内部的reduceByKey按key规约，然后这里传入某key当前批次的Seq/List,再计算当前批次的总和
      val currentCount = currValues.sum
      // 已累加的值
      val previousCount = prevValueState.getOrElse(0)
      // 返回累加后的结果，是一个Option[Int]类型
      Some(currentCount + previousCount)
    }

    val lines = ssc.socketTextStream(args(0), args(1).toInt)
    val words = lines.flatMap(_.split(" "))
    val pairs = words.map(word => (word, 1))

    //val currWordCounts = pairs.reduceByKey(_ + _)
    //currWordCounts.print()

    val totalWordCounts = pairs.updateStateByKey[Int](addFunc)
    totalWordCounts.print()

    ssc.start()
    ssc.awaitTermination()
  }
}

spark streaming updateStateByKey 用法