Search code examples
scalajson4s

Run time exception while trying to json serialize a 'val' or 'lazy val' Tuple field in grand parent Trait, in scala using json4s

I ran into a run time exception while serializing a case class, which extends a trait, which in turn extends another grandparent trait.

Problem occurs only when the grandparent trait contains a val or lazy val, which is a tuple. 

trait Trait0 {
  def a: Int

  lazy val b: (Int, Int) = (1, 2)
  // also errors if "val"
  // executes if "def" or just a simple type
}

trait Trait1 extends Trait0

case class Test(a: Int) extends Trait1

object Main {

  def main(args: Array[String]): Unit = {
    import org.json4s._
    import org.json4s.native.Serialization.write

    implicit val formats = DefaultFormats


    println(write(Test(1)))
  }
}

RunTime Exception I get is

Exception in thread "main" org.json4s.package$MappingException: Can't find field b from class com.adobe.formfactory.generator.Test at org.json4s.reflect.package$.fail(package.scala:95) at org.json4s.reflect.ScalaSigReader$.read$1(ScalaSigReader.scala:43) at org.json4s.reflect.ScalaSigReader$.$anonfun$readField$3(ScalaSigReader.scala:47) at scala.Option.getOrElse(Option.scala:121) at org.json4s.reflect.ScalaSigReader$.read$1(ScalaSigReader.scala:47) at org.json4s.reflect.ScalaSigReader$.readField(ScalaSigReader.scala:49) at org.json4s.reflect.Reflector$ClassDescriptorBuilder.$anonfun$fields$3(Reflector.scala:69) at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234) at scala.collection.mutable.ResizableArray.foreach(ResizableArray.scala:59) at scala.collection.mutable.ResizableArray.foreach$(ResizableArray.scala:52) at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48) at scala.collection.TraversableLike.map(TraversableLike.scala:234) at scala.collection.TraversableLike.map$(TraversableLike.scala:227) at scala.collection.AbstractTraversable.map(Traversable.scala:104) at org.json4s.reflect.Reflector$ClassDescriptorBuilder.fields(Reflector.scala:68) at org.json4s.reflect.Reflector$ClassDescriptorBuilder.properties(Reflector.scala:85) at org.json4s.reflect.Reflector$ClassDescriptorBuilder.result(Reflector.scala:184) at org.json4s.reflect.Reflector$.createDescriptor(Reflector.scala:53) at org.json4s.reflect.Reflector$.$anonfun$describe$1(Reflector.scala:48) at org.json4s.reflect.package$Memo.apply(package.scala:36) at org.json4s.reflect.Reflector$.describe(Reflector.scala:48) at org.json4s.Extraction$.decomposeObject$1(Extraction.scala:118) at org.json4s.Extraction$.internalDecomposeWithBuilder(Extraction.scala:228) at org.json4s.Extraction$.decomposeWithBuilder(Extraction.scala:64) at org.json4s.native.Serialization$.write(Serialization.scala:43) at org.json4s.native.Serialization$.write(Serialization.scala:37) at com.adobe.formfactory.generator.Main$.main(Main.scala:31) at com.adobe.formfactory.generator.Main.main(Main.scala)

Scala2.12.3
JDK1.8
json4s-native 3.5.3

I am guessing json4s isn't traversing up the super chain for tuples or other composite objects ?

If it were a case of providing custom serializer, the error, would mention that certain type cant be serialized.

Solution

  • I guess this is an existing bug since v3.4

    https://github.com/json4s/json4s/issues/221