Hadoop的Writerable在Spark无法序列化的问题

Spark序列化这块网上讲的比较少，自己还没来得及看这块代码，今天编程的时候遇到一个Hadoop的Writerable实现在Spark无法序列化的问题。我的代码如下：

object EntryApp extends App{

  val conf = new SparkConf().setAppName("cgbdata").setMaster("local")

  val sc = new SparkContext(conf)
  val hadoopConfig = new Configuration()
  hadoopConfig.set("sequoiadb.input.url","master:11810,slave1:11810,slave2:11810")
  hadoopConfig.set("sequoiadb.in.collectionspace","default")
  hadoopConfig.set("sequoiadb.in.collection","bar")
  val sdbRDD = sc.newAPIHadoopRDD[Object,BSONWritable,SequoiadbInputFormat](hadoopConfig,classOf[SequoiadbInputFormat],classOf[Object], classOf[BSONWritable])
  sdbRDD.map(_._2.getBson).collect.map(println)

  sc.stop()
}

这块代码执行报了如下错误。

Serialization stack:
    - object not serializable (class: org.bson.BasicBSONObject, value: { "_id" : { "$oid" : "55fe4caa4bb0b32e0e000000"} , "name" : "gaoxing"})
    - element of array (index: 0)
    - array (class [Lorg.bson.BSONObject;, size 2)
    at org.apache.spark.scheduler.DAGScheduler.org$apache$spark$scheduler$DAGScheduler$$failJobAndIndependentStages(DAGScheduler.scala:1273)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage$1.apply(DAGScheduler.scala:1264)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage$1.apply(DAGScheduler.scala:1263)
    at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
    at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
    at org.apache.spark.scheduler.DAGScheduler.abortStage(DAGScheduler.scala:1263)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed$1.apply(DAGScheduler.scala:730)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed$1.apply(DAGScheduler.scala:730)
    at scala.Option.foreach(Option.scala:236)
    at org.apache.spark.scheduler.DAGScheduler.handleTaskSetFailed(DAGScheduler.scala:730)
    at org.apache.spark.scheduler.DAGSchedulerEventProcessLoop.onReceive(DAGScheduler.scala:1457)
    at org.apache.spark.scheduler.DAGSchedulerEventProcessLoop.onReceive(DAGScheduler.scala:1418)
    at org.apache.spark.util.EventLoop$$anon$1.run(EventLoop.scala:48)

因为Spark默认使用Java的序列化，而Writeable没有实现序列化接口，导致整个问题的发生。通过google找到解决方式了。

val conf = new SparkConf().setAppName("cgbdata").setMaster("local").registerKryoClasses(Array(classOf[BSONWritable]))

查看相关代码：

  def registerKryoClasses(classes: Array[Class[_]]): SparkConf = {
    val allClassNames = new LinkedHashSet[String]()
    allClassNames ++= get("spark.kryo.classesToRegister", "").split(',').filter(!_.isEmpty)
    allClassNames ++= classes.map(_.getName)

    set("spark.kryo.classesToRegister", allClassNames.mkString(","))
    set("spark.serializer", classOf[KryoSerializer].getName)
    this
  }

调用registerKryoClasses这个方法，spark的序列化框架换成Kryo, 这个时候不需要实现Serializer接口了。当然里面具体怎么搞得不是太清楚。