Parsed JSON values do not match with class constructor

Question

My Runner code looks like

import java.io.File

import org.json4s._
import org.json4s.native.JsonMethods._

object WorkOrderParser {
  implicit val formats = DefaultFormats
  def get(workOrderJson: File): List[WorkOrderItem] = {
    parse(workOrderJson).extract[List[WorkOrderItem]]
  }

  def main(args: Array[String]) {
    println(WorkOrderParser.get(new File("src/main/resources/workConfigSample.json")))
  }
}

My case classes look like

import java.io.File

sealed trait FilePostProcessingAction

case object delete extends FilePostProcessingAction

case object move extends FilePostProcessingAction

case class WorkOrderItem(configName: String,
                         logSource: File,
                         logType: String,
                         afterProcessingFileAction: FilePostProcessingAction,
                         recursiveFind: Option[Boolean] = Some(false),
                         processZipFiles: Option[Boolean] = Some(false))

and my sample JSON looks like

[
  {
    "configName": "bluecoat",
    "logSource": "/root/fw1/logs/bc",
    "logType": "bluecoat",
    "recursiveFind": true,
    "processZipFiles": false,
    "afterProcessingFileAction": "delete"
  },
  {
    "configName": "mcAfee",
    "logSource": "/root/fw1/logs/mcafee",
    "logType": "mcafee",
    "recursiveFind": true,
    "processZipFiles": true,
    "afterProcessingFileAction": "delete"
  }
]

When I run this, I get

Exception in thread "main" org.json4s.package$MappingException: No usable value for logSource
Parsed JSON values do not match with class constructor
args=
arg types=
constructor=org.json4s.reflect.Executable@1fa268de
    at org.json4s.reflect.package$.fail(package.scala:93)
    at org.json4s.Extraction$ClassInstanceBuilder.org$json4s$Extraction$ClassInstanceBuilder$$buildCtorArg(Extraction.scala:509)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$14.apply(Extraction.scala:529)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$14.apply(Extraction.scala:529)
    at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:245)
    at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:245)
    at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
    at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
    at scala.collection.TraversableLike$class.map(TraversableLike.scala:245)
    at scala.collection.AbstractTraversable.map(Traversable.scala:104)
    at org.json4s.Extraction$ClassInstanceBuilder.org$json4s$Extraction$ClassInstanceBuilder$$instantiate(Extraction.scala:517)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$result$6.apply(Extraction.scala:564)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$result$6.apply(Extraction.scala:559)
    at org.json4s.Extraction$.org$json4s$Extraction$$customOrElse(Extraction.scala:573)
    at org.json4s.Extraction$ClassInstanceBuilder.result(Extraction.scala:559)
    at org.json4s.Extraction$.extract(Extraction.scala:394)
    at org.json4s.Extraction$CollectionBuilder$$anonfun$6.apply(Extraction.scala:403)
    at org.json4s.Extraction$CollectionBuilder$$anonfun$6.apply(Extraction.scala:403)
    at scala.collection.immutable.List.map(List.scala:273)
    at org.json4s.Extraction$CollectionBuilder.mkCollection(Extraction.scala:403)
    at org.json4s.Extraction$CollectionBuilder.result(Extraction.scala:423)
    at org.json4s.Extraction$.extract(Extraction.scala:377)
    at org.json4s.Extraction$.extract(Extraction.scala:43)
    at org.json4s.ExtractableJsonAstNode.extract(ExtractableJsonAstNode.scala:21)
    at com.logprocessor.processor.workOrder.WorkOrderParser$.get(WorkOrderParser.scala:11)
    at com.logprocessor.processor.workOrder.WorkOrderParser$.main(WorkOrderParser.scala:15)
    at com.logprocessor.processor.workOrder.WorkOrderParser.main(WorkOrderParser.scala)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: org.json4s.package$MappingException: Parsed JSON values do not match with class constructor
args=
arg types=
constructor=org.json4s.reflect.Executable@1fa268de
    at org.json4s.Extraction$ClassInstanceBuilder.org$json4s$Extraction$ClassInstanceBuilder$$instantiate(Extraction.scala:542)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$result$6.apply(Extraction.scala:564)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$result$6.apply(Extraction.scala:559)
    at org.json4s.Extraction$.org$json4s$Extraction$$customOrElse(Extraction.scala:573)
    at org.json4s.Extraction$ClassInstanceBuilder.result(Extraction.scala:559)
    at org.json4s.Extraction$.extract(Extraction.scala:394)
    at org.json4s.Extraction$ClassInstanceBuilder.org$json4s$Extraction$ClassInstanceBuilder$$buildCtorArg(Extraction.scala:497)
    ... 30 more

However, when I change type in my case classes to String (for logSource and afterProcessingFileAction), it works

What am I doing wrong? I am using https://github.com/json4s/json4s for this

Answer 1

A few years too late maybe, but i see 2k views so let's answer this :)

This is because json4s is looking for how to deserialize a List[WorkOrderItem] and it can't find the constructor matching extract[T], in your case extract[List[WorkOrderItem]].

I believe you need to create a custom deserializer and register this as one of the supported formats. NOTE: There could be other ways around this, for example using Hints or other features, but I only started with json4s yesterday so I'm a bit of a noob..

For example -

1. Create your case class -

case class DynamicStringList(values: List[String]) {
  def show() {
    values.foreach(println)
  }
}

2. Create your serializer. Below a working example -

case object DynamicStringListSerializer extends CustomSerializer[DynamicStringList] (format => ({
  case JString(stringValue) => DynamicStringList(List(stringValue))
  case JArray(stringValues) => {
    implicit val formats = DefaultFormats
    def jsonJValueToString(jsonString: JValue)(implicit formats: Formats) : String = {
      jsonString.extract[String]
    }
    val dynamicList = stringValues.map(jsonJValueToString).toList
    DynamicStringList(dynamicList) //DynamicStringArray.toArray(stringValues)
  }
}, {
  // TODO - This is the serialize function to JArray, however we will probably never use it so not done for now
  case dynamicList: DynamicStringList => JNothing
}
))

3. Register this as a supported format in the object/class you need it -

import org.json4s.DefaultFormats
import com.myserializers.DynamicStringListSerializer

object MyJSONUtils {   
    implicit val formats = DefaultFormats + DynamicStringListSerializer

4. Do stuff (assuming you have all the other json imports you need)

parse(json_message_as_string).extract[DynamicStringList]