JSON Serializing Scala Case Class to only strings and ints - json

Question

I have a need to serialize a handful of case classes to only strings and ints. Meaning, if there's a nested type, it gets serialized as the stringified version of a JSON object, not a JSON object.
Example:
case class Deepest(someNum: Int)
case class Inner(superDeep: Deepest)
case class Outer(aValue: Int, aNestedValue: Inner)
Serializing an instance of Outer Would result in (or something similar)
{
"Outer": {
"aValue": 5,
"aNestedValue": "{ \"superDeep\": .... }"
}
}
Is this possible?

Answer 1

Using jsoniter-scala is the simplest and most efficient way to do it with Scala.
Add dependencies:
libraryDependencies ++= Seq(
// Use the %%% operator instead of %% for Scala.js
"com.github.plokhotnyuk.jsoniter-scala" %% "jsoniter-scala-core" % "2.12.0",
// Use the "provided" scope instead when the "compile-internal" scope is not supported
"com.github.plokhotnyuk.jsoniter-scala" %% "jsoniter-scala-macros" % "2.12.0" % "compile-internal"
)
Use a custom codec from this snippet:
import com.github.plokhotnyuk.jsoniter_scala.macros._
import com.github.plokhotnyuk.jsoniter_scala.core._
object Example01 {
sealed trait Message
case class Deepest(someNum: Int)
case class Inner(superDeep: Deepest)
case class Outer(aValue: Int, aNestedValue: Inner) extends Message
implicit val innerCodec: JsonValueCodec[Inner] = new JsonValueCodec[Inner] {
private val codec: JsonValueCodec[Inner] = JsonCodecMaker.make
override def decodeValue(in: JsonReader, default: Inner): Inner =
readFromStringReentrant(in.readString(null))(codec)
override def encodeValue(x: Inner, out: JsonWriter): Unit =
out.writeVal(writeToStringReentrant(x)(codec))
override def nullValue: Inner = null
}
implicit val messageCodec: JsonValueCodec[Message] =
JsonCodecMaker.make(CodecMakerConfig.withDiscriminatorFieldName(None))
def main(args: Array[String]): Unit = {
val message = readFromString[Message](
"""{
| "Outer": {
| "aValue": 5,
| "aNestedValue": "{ \"superDeep\": { \"someNum\": 1 } }"
| }
|}""".stripMargin)
println(writeToString[Message](message, WriterConfig.withIndentionStep(4)))
}
}
Expected output:
{
"Outer": {
"aValue": 5,
"aNestedValue": "{\"superDeep\":{\"someNum\":1}}"
}
}
If more than one type should be stringified you can define a function that takes a regular codec and return a codec that stringify output of original one:
def makeStringifyingCodec[A](codec: JsonValueCodec[A]): JsonValueCodec[A] =
new JsonValueCodec[A] {
override def decodeValue(in: JsonReader, default: A): A =
readFromStringReentrant(in.readString(null))(codec)
override def encodeValue(x: A, out: JsonWriter): Unit =
out.writeVal(writeToStringReentrant(x)(codec))
override def nullValue: A = null.asInstanceOf[A]
}
And use it for field types of the Outer class:
implicit val innerCodec: JsonValueCodec[Inner] =
makeStringifyingCodec(JsonCodecMaker.make[Inner])
implicit val messageCodec: JsonValueCodec[Message] =
JsonCodecMaker.make(CodecMakerConfig.withDiscriminatorFieldName(None))