Java和Kryo序列化，Java.io.OptionalDataException

我已经在SparkConf中将Kryo Serializer设置为默认序列化程序，Spark UI也确认了这一点，但在Spark日志中我得到了这个异常

java.io.OptionalDataException
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1370)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
at scala.collection.immutable.$colon$colon.readObject(List.scala:366)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1017)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1893)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1990)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1915)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1990)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1915)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
at org.apache.spark.scheduler.DirectTaskResult$$anonfun$readExternal$1.apply$mcV$sp(TaskResult.scala:74)
at org.apache.spark.util.Utils$.tryOrIOException(Utils.scala:993)
at org.apache.spark.scheduler.DirectTaskResult.readExternal(TaskResult.scala:58)
at java.io.ObjectInputStream.readExternalData(ObjectInputStream.java:1837)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1796)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
at org.apache.spark.serializer.JavaDeserializationStream.readObject(JavaSerializer.scala:62)
at org.apache.spark.serializer.JavaSerializerInstance.deserialize(JavaSerializer.scala:81)
at org.apache.spark.scheduler.TaskResultGetter$$anon$2$$anonfun$run$1.apply$mcV$sp(TaskResultGetter.scala:50)
at org.apache.spark.scheduler.TaskResultGetter$$anon$2$$anonfun$run$1.apply(TaskResultGetter.scala:49)
at org.apache.spark.scheduler.TaskResultGetter$$anon$2$$anonfun$run$1.apply(TaskResultGetter.scala:49)
at org.apache.spark.util.Utils$.logUncaughtExceptions(Utils.scala:1468)
at org.apache.spark.scheduler.TaskResultGetter$$anon$2.run(TaskResultGetter.scala:48)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)

我有两个问题：

1-为什么仍在使用java序列化程序？
2-如何解决java.io.OptionalDataException

根据，我知道java.io.OptionalDataException的原因，但无法解决

这是我的班级：

    class GeometryWritable(var geometry: Geometry) extends Writable with Externalizable with KryoSerializable {

       def this() = this(null)

       override def write(dataOutput: DataOutput) {
          val bytes = GeometryEngine.geometryToEsriShape(geometry)
          dataOutput.writeInt(bytes.length);
          dataOutput.write(bytes);
      }
      override def readFields(dataInput: DataInput) {
          val bytesArray: Array[Byte] = new Array[Byte](dataInput.readInt())
          dataInput.readFully(bytesArray)
          geometry = GeometryEngine.geometryFromEsriShape(bytesArray, Geometry.Type.Unknown);
      }
      /**
       * override writeExternal (as class is extends by Writable interface)
       *
       * @param dataOutPut, Data Output Stream where data has to pushed
       * @return Unit
       */
      @throws(classOf[IOException])
      override def writeExternal(dataOutput: ObjectOutput) {
         val bytes = GeometryEngine.geometryToEsriShape(geometry)
         dataOutput.writeInt(bytes.length);
         dataOutput.write(bytes);
      }
      /**
       * override readFields (as class is extends by Writable interface)
       *
       * @param dataInput, Data Input Stream from where data has to read
       * @return Unit
       */
       @throws(classOf[IOException])
       @throws(classOf[ClassNotFoundException])
       override def readExternal(dataInput: ObjectInput) {
           val bytesArray: Array[Byte] = new Array[Byte](dataInput.readInt())
           dataInput.readFully(bytesArray)
           geometry = GeometryEngine.geometryFromEsriShape(bytesArray, Geometry.Type.Unknown)
       }
       def write(kryo: Kryo, output: Output) {
           val bytes = GeometryEngine.geometryToEsriShape(geometry)
           output.writeInt(bytes.length);
           output.write(bytes);
       }

       def read(kryo: Kryo, input: Input) {
          val bytesArray: Array[Byte] = new Array[Byte](input.readInt())
          input.read(bytesArray, 0, bytesArray.length)
          geometry = GeometryEngine.geometryFromEsriShape(bytesArray, Geometry.Type.Unknown)
       }
    }