CODEWITHSUNDEEP
jsonscalajackson
yhylord
yhylord

Reputation: 420

Jackson doesn't serialize field defined by `def`

Following the approach in Easy JSON (un)marshalling in Scala with Jackson, I have defined a JsonUtil class:

import com.fasterxml.jackson.databind.{DeserializationFeature, JsonNode, ObjectMapper}
import com.fasterxml.jackson.module.scala.DefaultScalaModule
import com.fasterxml.jackson.module.scala.experimental.ScalaObjectMapper

object JsonUtil {
  val mapper = new ObjectMapper() with ScalaObjectMapper
  mapper.registerModule(DefaultScalaModule)
  mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
  mapper.enable(DeserializationFeature.USE_LONG_FOR_INTS)

  def toJsonNode[T](elem: T): JsonNode = mapper.valueToTree(elem)
}

And now I want to serialize a class containing an Int and another Int with double the value:

import JsonUtil.toJsonNode

trait X {
  def x: Int
  def doubleX: Int = x * 2
}

case class Three() extends X {
  val x = 3
}

println(toJsonNode(Three()))
// {"x":3}
println(Three().doubleX)
// 6

I realize that Jackson might not recognize a field defined by def. However, defining doubleX by def instead of val ensures that its value is always correct. Any workaround to make def and Jackson compatible?

Upvotes: 0

Views: 107

Answers (1)

Alexey Romanov
Alexey Romanov

Reputation: 170755

def doesn't define a field, it's a method. Just annotate the def with @JsonProperty and Jackson should consider it as a getter for a "logical property".

Upvotes: 2

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