Scala json4s sealed trait as enums - scala

Question

We have our status defined as:
sealed trait Status
case object Status {
case object StatusA extends Status
case object StatusB extends Status
case object StatusC extends Status
}
Our status looks like:
val status = Status.StatusA
Is there any way to (de)serialize that kind of structure with predefined json4s fomratters?
We tried with defult formatter like:
implicit val formats = new org.json4s.DefaultFormats
and it did not work. Next we tried to use ext provided by json4s with Enum support:
implicit val formats = org.json4s.DefaultFormats + new org.json4s.ext.EnumSerializer(Status)
and it did not work again. We had to totally change the structure of the sealed trait to actual Enumerations. Is there any way to do it with case classes?

Answer 1

Here is a full working example, I changed your classes a bit to make the example simpler and this way you can use the "name" in different ways you can actually omit the "def name", but in this case you will need to change the serialiser a bit. The second Serializer is just below.
sealed trait Status {
def name: String
}
case object Status {
def apply(name: String): Status = name match {
case StatusA.name => StatusA
case StatusB.name => StatusB
case StatusC.name => StatusC
case _ => throw new UnsupportedOperationException("Unknown value")
}
}
case object StatusA extends Status {
override val name = "StatusA"
}
case object StatusB extends Status {
override val name = "StatusB"
}
case object StatusC extends Status {
override val name = "StatusC"
}
class StatusSerializer extends CustomSerializer[Status](formats =>
( {
case JString(s) => Status(s)
case JNull => throw new UnsupportedOperationException("No status specified")
}, {
case status: Status => JString(status.name)
})
)
case class SimpleRichObject(someString: String, someInt: Int, statuses: List[Status])
object Test extends App {
implicit val formats = DefaultFormats + new StatusSerializer
val obj = SimpleRichObject("Answer to life the universe and everything", 42, List(StatusA, StatusB, StatusC))
def toCompactJsonString(any: Any) = {
JsonMethods.compact(JsonMethods.render(Extraction.decompose(any)))
}
def toPrettyJsonString(any: Any) = {
JsonMethods.pretty(JsonMethods.render(Extraction.decompose(any)))
}
/** To Json */
println(s"Compact json:\n${toCompactJsonString(obj)}")
println(s"Pretty json:\n${toPrettyJsonString(obj)}")
/** From Json */
val json =
"""{
| "someString":"Here is a another String",
| "someInt":1234,
| "statuses":["StatusA","StatusB"]
|}""".stripMargin
val richObj = JsonMethods.parse(json).extract[SimpleRichObject]
println(s"Rich object toString: $richObj")
}
Here is the second Serializer, by using the second one you don't need to define extra code in your "Enums"
class SecondStatusSerializer extends CustomSerializer[Status](formats =>
( {
case JString(s) => s match {
case "StatusA" => StatusA
case "StatusB" => StatusB
case "StatusC" => StatusC
}
case JNull => throw new UnsupportedOperationException("No status specified")
}, {
case status: Status => status match {
case StatusA => JString("StatusA")
case StatusB => JString("StatusB")
case StatusC => JString("StatusC")
}
})
)
And here how this one looks when run, compact json:
{"someString":"Answer to life the universe and everything","someInt":42,"statuses":["StatusA","StatusB","StatusC"]}
Pretty json:
{
"someString":"Answer to life the universe and everything",
"someInt":42,
"statuses":["StatusA","StatusB","StatusC"]
}
Rich object toString: SimpleRichObject(Here is a another String,1234,List(StatusA, StatusB))