执行火花流时的"java.io.NotSerializableException: org.apache.spark.streaming.StreamingContext“

Question

当我在纱线上执行火花流应用程序时，我继续收到以下错误

为什么会发生错误，如何解决？任何建议都会有帮助的，谢谢~

15/05/07 11:11:50 INFO dstream.StateDStream: Marking RDD 2364 for time 1430968310000 ms for checkpointing
    15/05/07 11:11:50 INFO scheduler.JobScheduler: Added jobs for time 1430968310000 ms
    15/05/07 11:11:50 INFO scheduler.JobGenerator: Checkpointing graph for time 1430968310000 ms
    15/05/07 11:11:50 INFO streaming.DStreamGraph: Updating checkpoint data for time 1430968310000 ms
    15/05/07 11:11:50 INFO streaming.DStreamGraph: Updated checkpoint data for time 1430968310000 ms
    15/05/07 11:11:50 ERROR actor.OneForOneStrategy: org.apache.spark.streaming.StreamingContext
    java.io.NotSerializableException: org.apache.spark.streaming.StreamingContext
            at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)
            at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
            at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
            at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
            at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
            at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
            at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
            at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
            at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
            at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
            at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
            at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
            at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)

星星之流应用程序代码如下所示，我将在火花壳中执行它。

    import kafka.cluster.Cluster
import kafka.serializer.StringDecoder
import org.apache.spark.storage.StorageLevel
import org.apache.spark.streaming.kafka.KafkaUtils
import org.apache.spark.streaming.{Duration, StreamingContext}
import org.apache.spark.rdd.RDD
import org.apache.spark.streaming.StreamingContext._

val updateFunc = (values: Seq[Int], state: Option[Int]) => {
  Some(0)
}

val ssc = new StreamingContext(sc,
  new Duration(5000))
ssc.checkpoint(".")

val lines = KafkaUtils.createStream(ssc, "10.1.10.21:2181", "kafka_spark_streaming", Map("hello_test" -> 3))

val uuidDstream = lines.transform(rdd => rdd.map(_._2)).map(x => (x, 1)).updateStateByKey[Int](updateFunc)
uuidDstream.count().print()

ssc.start()
ssc.awaitTermination()

Answer 1

在val updateFunc闭包中使用的对updateStateByKey的引用是将该实例的其余部分拖到闭包中，并将StreamingContext与其一起使用。

有两种选择：

• 快速修复:声明流上下文瞬态=> @transient val ssc= ...也是注释dstream声明以及@transient的好主意。
• 更好的解决方法:将函数放在单独的对象中。

如下所示：

case object TransformFunctions {
    val updateFunc = ???
}