在spark-streaming中解析json

Question

我是spark的新手，我正在尝试从kafka主题中接收一个被构造为json的DStream，我想解析每个json的内容。我收到的json是这样的：

{"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":" "}

我试图只提取ident字段，至少现在是这样，并且我正在使用lift-json库来解析de数据。我的程序看起来像这样：

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()
 }
}

但它抛出了下面的异常：

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)

问题是，如果不使用spark (从文件中读取)运行相同的程序，它就能完美地工作。当我试图将它放入spark程序中时，问题就开始了。另外，如果我将解析器函数更改为如下所示：

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

它也是有效的。但是当我试图提取实际的字符串时，我得到了同样的错误。

谢谢你的帮助。我希望我已经解释得很好了。

Answer 1

这是因为您缺少序列化/反序列化记录所需的scala反映依赖项。尝试添加与spark版本匹配的scala反射jar。

提示："org.scala-lang“% "scala-reflect”% Version.scala

Answer 2

哦，一个很好的老问题:-)

基本上，这表明存在版本问题:您的一个依赖项与您当前使用的Scala编译器不兼容。你在2.10吗？

试着用谷歌搜索短语"NoClassDefFoundError: scala/reflect/ClassManifest"，我相信你会找到足够多的关于这个问题的描述。