在火花流中解析 json

Question

I'm pretty new to spark and I'm trying to receive a DStream structured as a json from a kafka topic and I want to parse the content of each json. The json I receive is something like this:

{"type":"position","ident":"IBE32JZ","air_ground":"A","alt":"34000","clock":"1409733420","id":"IBE32JZ-1409715361-ed-0002:0","gs":"446","heading":"71","lat":"44.50987","lon":"2.98972","reg":"ECJRE","squawk":"1004","updateType":"A","altChange":" "}

I'm trying to extract the ident field only, at least for now and I'm using lift-json library to parse the data. My program looks like this:

object ScalaExample {
    val kafkaHost = "localhost"
    val kafkaPort = 9092
    val zookeeperHost = "localhost"
    val zookeeperPort = 2181

    implicit val formats = DefaultFormats
    case class PlaneInfo(ident: String)


    def parser(json: String): String = {
        val parsedJson = parse(json)
        val m = paso1.extract[PlaneInfo]
        return m.ident
    }

    def main(args : Array[String]) {
        val zkQuorum = "localhost:2181"
        val group = "myGroup"
        val topic = Map("flightStatus" -> 1)
        val sparkContext = new SparkContext("local[4]", "KafkaConsumer")
        val ssc = new StreamingContext(sparkContext, Seconds(10))


        val json = KafkaUtils.createStream(ssc, zkQuorum, group, topic)

        val id = json.map(_._2).map(parser)

        id.print

        ssc.start()
 }
}

but it throws me the exception below:

java.lang.NoClassDefFoundError: scala/reflect/ClassManifest
    at net.liftweb.json.JsonAST$JValue.extract(JsonAST.scala:300)
    at aero.catec.stratio.ScalaExample$.parser(ScalaExample.scala:33)
    at aero.catec.stratio.ScalaExample$$anonfun$2.apply(ScalaExample.scala:48)
    at aero.catec.stratio.ScalaExample$$anonfun$2.apply(ScalaExample.scala:48)
    at scala.collection.Iterator$$anon$11.next(Iterator.scala:328)
    at scala.collection.Iterator$$anon$10.next(Iterator.scala:312)
    at scala.collection.Iterator$class.foreach(Iterator.scala:727)
    at scala.collection.AbstractIterator.foreach(Iterator.scala:1157)
    at scala.collection.generic.Growable$class.$plus$plus$eq(Growable.scala:48)
    at scala.collection.mutable.ArrayBuffer.$plus$plus$eq(ArrayBuffer.scala:103)
    at scala.collection.mutable.ArrayBuffer.$plus$plus$eq(ArrayBuffer.scala:47)
    at scala.collection.TraversableOnce$class.to(TraversableOnce.scala:273)
    at scala.collection.AbstractIterator.to(Iterator.scala:1157)
    at scala.collection.TraversableOnce$class.toBuffer(TraversableOnce.scala:265)
    at scala.collection.AbstractIterator.toBuffer(Iterator.scala:1157)
    at scala.collection.TraversableOnce$class.toArray(TraversableOnce.scala:252)
    at scala.collection.AbstractIterator.toArray(Iterator.scala:1157)
    at org.apache.spark.rdd.RDD$$anonfun$28.apply(RDD.scala:1003)
    at org.apache.spark.rdd.RDD$$anonfun$28.apply(RDD.scala:1003)
    at org.apache.spark.SparkContext$$anonfun$runJob$4.apply(SparkContext.scala:1083)
    at org.apache.spark.SparkContext$$anonfun$runJob$4.apply(SparkContext.scala:1083)
    at org.apache.spark.scheduler.DAGScheduler.runLocallyWithinThread(DAGScheduler.scala:575)
    at org.apache.spark.scheduler.DAGScheduler$$anon$1.run(DAGScheduler.scala:560)
Caused by: java.lang.ClassNotFoundException: scala.reflect.ClassManifest
    at java.net.URLClassLoader$1.run(URLClassLoader.java:372)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)

The thing is that if a run the same without using spark (reading from a file) it works perfectly. The problem starts when I try to put it in a spark program. Also, if I change the parser function to something like this:

def parser(json: String): JValue = {
  val parsedJson = parse(json)
  return (parsedJson \\ "ident")
}

It also works. But when I try to extract the actual String, I get the same error.

Thank you for your help. I hope I had explained it well.

Answer 1

this happens because you are missing a scala reflect dependence needed to serialize/deserialize the record. Try to add the scala reflect jar that match the spark version.

Tip: "org.scala-lang" % "scala-reflect" % Version.scala

Answer 2

Oh, a good old issue :-)

Basically this indicates a version problem: one of your dependencies is not compatible with the Scala compiler you are currently using. Are you on 2.10?

Try Googling the phrase "NoClassDefFoundError: scala/reflect/ClassManifest" , I'm sure you will find more than enough description about the issue.