Recursive type conversion jackson json parser

Question

I'm using Jackson to parse json string to scala case class instance. Here's my code

import com.fasterxml.jackson.databind.{DeserializationFeature, ObjectMapper}
import com.fasterxml.jackson.module.scala.DefaultScalaModule
import scala.reflect.{ClassTag, _}

object JsonUtil {
  val jacksonMapper = new ObjectMapper()
  jacksonMapper.registerModule(DefaultScalaModule)
  jacksonMapper.configure(DeserializationFeature.FAIL_ON_MISSING_CREATOR_PROPERTIES, false)
  jacksonMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)

  def toJson(value: Map[Symbol, Any]): String = {
    toJson(value map { case (k,v) => k.name -> v})
  }

  def toJson(value: Any): String = {
    jacksonMapper.writeValueAsString(value)
  }

  def fromJson[T: ClassTag](json: String): T = {
    jacksonMapper.readValue[T](json, classTag[T].runtimeClass.asInstanceOf[Class[T]])
  }
}

and this's the json parsing error

case class Person(name: String, age: Long, score: List[Long])
val person = JsonUtil.fromJson[Person]("""{"name": 123654,"age":23, "score": [6,7,9]}""")
person.name
person.score
person.score.head
res0: String = 123654
java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Long
    at scala.runtime.BoxesRunTime.unboxToLong(ws.sc93376:101)
    at #worksheet#.#worksheet#(ws.sc93376:35)

I know jackson is smart enough to convert between numeric types, string to numeric and vice versa, but seemingly it only works for non-collection situation.

How can I do better, that forces jackson recursively converts type inside collection?

Answer 1

You have to add this annotation before score: List[Long] :

@JsonDeserialize(contentAs = classOf[java.lang.Long])

Source: https://github.com/FasterXML/jackson-module-scala/wiki/FAQ