Spark: mapPartitions object not serializable

Question

I'm pretty new to spark and scala. I'm trying to run a small program to better understand mapPartitioins. However when I run the code below, I get an error that the class isn't serializable. I tried putting the code in a companion class, but that didn't work either. I also tried removing private from everything but that didn't work either. I'm at a loss as to why this isn't working.

import java.sql.Date

import org.apache.spark.SparkConf
import org.apache.spark.rdd.RDD
import org.apache.spark.sql.functions._
import org.apache.spark.sql.{Dataset, Row, SparkSession}

import scala.collection.mutable

object DataSetTest {

  val spark: SparkSession = createSparkContext()

  def main(args: Array[String]): Unit ={
    import spark.implicits._
    val refDate = new Date(System.currentTimeMillis())
    val events : Dataset[Row] = Seq(
      ("Q", "A", 5, 10),
      ("N", "A", 8, 11)
    ).toDF("type", "symbol", "birth", "death")
      .repartition(col("refDate"), col("symbol"))
      .sort(col("birth"))

    events.show()

    val matches : Dataset[NbboQuoteMatch] = events.mapPartitions(partition =>
      return processTInsidePartition(partition)
    )

    matches.show()
  }

  val processTInsidePartition = (partition: Iterator[Row]) => {
    import spark.implicits._
    val results  = new mutable.ArrayBuffer[NbboQuoteMatch]
    val rdd: RDD[NbboQuoteMatch] = spark.sparkContext.parallelize(results.toList)


    spark.createDataset[NbboQuoteMatch](rdd)
  }


  case class NbboQuoteMatch (val nbbo: Nbbo, val quote: Quote)

  trait Event{
    def getBirth(): Long
    def getDeath() : Long
    def getType() : String
  }

  case class Nbbo( val symbol: String, val birth: Long, val death: Long) extends Event {
    override def getBirth(): Long = birth
    override def getDeath(): Long = death
    override def getType(): String = "Q"
  }

  case class Quote ( val symbol: String, val birth: Long, val death: Long) extends Event{
    override def getDeath(): Long = death
    override def getBirth(): Long = birth
    override def getType(): String = "N"
  }


  def createSparkContext(): SparkSession ={
    val rv : SparkSession  = SparkSession.builder()
      .appName("abc")
      .config(new SparkConf())
      .enableHiveSupport()
      .config("spark.master", "local[*]")
      .config("hive.exec.dynamic.partition", "true")
      .config("hive.exec.dynamic.partition.mode", "nonstrict")
      .config("spark.executor.instances", 8).getOrCreate()

    return rv;
  }

}

Error

Exception in thread "main" org.apache.spark.SparkException: Job aborted due to stage failure: Task not serializable: java.io.NotSerializableException: sandbox.etp.DataSetTest$
Serialization stack:
    - object not serializable (class: sandbox.etp.DataSetTest$, value: sandbox.etp.DataSetTest$@7d1ccdfe)
    - element of array (index: 0)
    - array (class [Ljava.lang.Object;, size 2)
    - field (class: java.lang.invoke.SerializedLambda, name: capturedArgs, type: class [Ljava.lang.Object;)
    - object (class java.lang.invoke.SerializedLambda, SerializedLambda[capturingClass=class sandbox.etp.DataSetTest$, functionalInterfaceMethod=scala/Function1.apply:(Ljava/lang/Object;)Ljava/lang/Object;, implementation=invokeStatic sandbox/etp/DataSetTest$.$anonfun$main$1:(Lsandbox/etp/DataSetTest$;Ljava/lang/Object;Lscala/collection/Iterator;)Lscala/runtime/Nothing$;, instantiatedMethodType=(Lscala/collection/Iterator;)Lscala/runtime/Nothing$;, numCaptured=2])
    - writeReplace data (class: java.lang.invoke.SerializedLambda)
    - object (class sandbox.etp.DataSetTest$$$Lambda$17/1227659410, sandbox.etp.DataSetTest$$$Lambda$17/1227659410@4d4c4b14)
    - field (class: org.apache.spark.sql.execution.MapPartitionsExec, name: func, type: interface scala.Function1)
    - object (class org.apache.spark.sql.execution.MapPartitionsExec, MapPartitions sandbox.etp.DataSetTest$$$Lambda$17/1227659410@4d4c4b14, obj#40: sandbox.etp.DataSetTest$NbboQuoteMatch
+- DeserializeToObject createexternalrow(type#11.toString, staticinvoke(class org.apache.spark.sql.catalyst.util.DateTimeUtils$, ObjectType(class java.sql.Date), toJavaDate, refDate#12, true, false), symbol#13.toString, birth#14, death#15, StructField(type,StringType,true), StructField(refDate,DateType,true), StructField(symbol,StringType,true), StructField(birth,IntegerType,false), StructField(death,IntegerType,false)), obj#39: org.apache.spark.sql.Row
   +- *(1) Sort [birth#14 ASC NULLS FIRST], true, 0
      +- Exchange rangepartitioning(birth#14 ASC NULLS FIRST, 200)
         +- Exchange hashpartitioning(refDate#12, symbol#13, 200)
            +- LocalTableScan [type#11, refDate#12, symbol#13, birth#14, death#15]

Answer 1

You are using processTInsidePartition inside mapPartitions closure.

Try extending Serializable interface as follows-

object DataSetTest extends Serializable {
...
...
}