CODEWITHSUNDEEP
scalaserializationjson4s
Evgeny Veretennikov
Evgeny Veretennikov

Reputation: 4239

json4s: unable to parse JSON with renamed field

I need to serialize and then deserialize case class object with field "name" from JSON, which has "animalname" field instead of "name". Serializing works ok, but deserializing not. I used FieldSerializer with renameTo() and renameFrom():

import org.json4s._
import org.json4s.FieldSerializer._
import org.json4s.jackson.Serialization._

case class WildDog(name: String)
val dogSerializer = FieldSerializer[WildDog](
  renameTo("name", "animalname"),
  renameFrom("animalname", "name"))
implicit val formats = DefaultFormats + dogSerializer
// serialize
val json = write(WildDog("beefy")) // {"animalname":"beefy"}, as expected
// try to deserialize
val dog = parse(json).extract[WildDog] // expected: Dog("beefy")

Actually, extract() throws exception:

org.json4s.package$MappingException: No usable value for name
Did not find value which can be converted into java.lang.String
    at org.json4s.reflect.package$.fail(ws.sc:94)
    at org.json4s.Extraction$ClassInstanceBuilder.org$json4s$Extraction$ClassInstanceBuilder$$buildCtorArg(ws.sc:409)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$11.apply(ws.sc:417)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$11.apply(ws.sc:417)
    at scala.collection.TraversableLike$$anonfun$map$1.apply(ws.sc:240)
    at scala.collection.TraversableLike$$anonfun$map$1.apply(ws.sc:240)
    at scala.collection.mutable.ResizableArray$class.foreach(ws.sc:55)
    at scala.collection.mutable.ArrayBuffer.foreach(ws.sc:43)
    at scala.collection.TraversableLike$class.map(ws.sc:240)
    at scala.collection.AbstractTraversable.map(ws.sc:101)
    at org.json4s.Extraction$ClassInstanceBuilder.org$json4s$Extraction$ClassInstanceBuilder$$instantiate(ws.sc:417)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$result$6.apply(ws.sc:445)
    at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$result$6.apply(ws.sc:442)
    at org.json4s.Extraction$.org$json4s$Extraction$$customOrElse(ws.sc:454)
    at org.json4s.Extraction$ClassInstanceBuilder.result(ws.sc:442)
    at org.json4s.Extraction$.extract(ws.sc:304)
    at org.json4s.Extraction$.extract(ws.sc:38)
    at org.json4s.ExtractableJsonAstNode.extract(ws.sc:17)

How to deserialize this JSON correctly?

update: I use Scala 2.10, json4s 3.2.5.

update 2: I use this Maven dependency for json4s:

<dependency>
    <groupId>org.json4s</groupId>
    <artifactId>json4s-jackson_2.10</artifactId>
    <version>3.2.5</version>
</dependency>

Upvotes: 1

Views: 1706

Answers (1)

pjames
pjames

Reputation: 302

try val dog = read[WildDog](json) instead of val dog = parse(json).extract[WildDog]

The github page - https://github.com/json4s/json4s has some other good examples too.

Edit:

Working versions:
Scala 2.10 && org.json4s.jackson >= 3.5.0
Scala 2.11 && org.json4s.jackson >= 3.2.5

I have not checked earlier versions for Scala 2.10, but the exception exists when I am using 3.2.5.

Also, I am able to get val dog = parse(json).extract[WildDog] to work, but you must import the JsonMethods -> import org.json4s.jackson.JsonMethods.parse

Upvotes: 2

Related Questions