Alan Lam Alan Lam - 2 months ago 8
Scala Question

Scala: Xtream complains object not serializable

I have the following case classes defined and i would like to print out

ClientData
in xml format using xstream.

case class Address(addressLine1: String,
addressLine2: String,
city: String,
provinceCode: String,
country: String,
addressTypeDesc: String) extends Serializable{

}

case class ClientData(title: String,
firstName: String,
lastName: String,
addrList:Option[List[Address]]) extends Serializable{

}


object ex1{
def main(args: Array[String]){
...
...
...

// In below, x is Try[ClientData]
val xstream = new XStream(new DomDriver)
newClientRecord.foreach(x=> if (x.isSuccess) println(xstream.toXML(x.get)))

}
}


And when the program execute the line to print each ClientData in xml format, I am getting the runtime error below. Please help.

Exception in thread "main" org.apache.spark.SparkException: Task not serializable
at org.apache.spark.util.ClosureCleaner$.ensureSerializable(ClosureCleaner.scala:304)
at org.apache.spark.util.ClosureCleaner$.org$apache$spark$util$ClosureCleaner$$clean(ClosureCleaner.scala:294)
at org.apache.spark.util.ClosureCleaner$.clean(ClosureCleaner.scala:122)
at org.apache.spark.SparkContext.clean(SparkContext.scala:2055)
at org.apache.spark.rdd.RDD$$anonfun$foreach$1.apply(RDD.scala:911)
at org.apache.spark.rdd.RDD$$anonfun$foreach$1.apply(RDD.scala:910)
at org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:150)
at org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:111)
at org.apache.spark.rdd.RDD.withScope(RDD.scala:316)
at org.apache.spark.rdd.RDD.foreach(RDD.scala:910)
at lab9$.main(lab9.scala:63)
at lab9.main(lab9.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)
Caused by: java.io.NotSerializableException: com.thoughtworks.xstream.XStream
Serialization stack:
- object not serializable (class: com.thoughtworks.xstream.XStream, value: com.thoughtworks.xstream.XStream@51e94b7d)
- field (class: lab9$$anonfun$main$1, name: xstream$1, type: class com.thoughtworks.xstream.XStream)
- object (class lab9$$anonfun$main$1, <function1>)
at org.apache.spark.serializer.SerializationDebugger$.improveException(SerializationDebugger.scala:40)
at org.apache.spark.serializer.JavaSerializationStream.writeObject(JavaSerializer.scala:47)
at org.apache.spark.serializer.JavaSerializerInstance.serialize(JavaSerializer.scala:101)
at org.apache.spark.util.ClosureCleaner$.ensureSerializable(ClosureCleaner.scala:301)
... 16 more

Answer

It isn't XStream which complains, it's Spark. You need to define xstream variable inside the task:

newClientRecord.foreach { x=> 
  if (x.isSuccess) {
    val xstream = new XStream(new DomDriver)
    println(xstream.toXML(x.get)) 
  }
}

if XStream is sufficiently cheap to create;

newClientRecord.foreachPartition { xs => 
  val xstream = new XStream(new DomDriver)
  xs.foreach { x =>
    if (x.isSuccess) {
      println(xstream.toXML(x.get)) 
    }
  }
}

otherwise.

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