serializing objects to json with play.api.libs.json

Question

I'm trying to serialize some relatively simple models into json. For example, I'd like to get the json representation of:

case class User(val id: Long, val firstName: String, val lastName: String, val email: Option[String]) {
    def this() = this(0, "","", Some(""))
}

Do i need to write my own Format[User] with the appropriate reads and writes methods or is there some other way? I've looked at https://github.com/playframework/Play20/wiki/Scalajson but I'm still a bit lost.

score 24 · Accepted Answer · edited Jul 05 '22 at 14:03

24

Yes, writing your own Format instance is the recommended approach. Given the following class, for example:

case class User(
  id: Long, 
  firstName: String,
  lastName: String,
  email: Option[String]
) {
  def this() = this(0, "","", Some(""))
}

The instance might look like this:

import play.api.libs.json._

implicit object UserFormat extends Format[User] {
  def reads(json: JsValue) = User(
    (json \ "id").as[Long],
    (json \ "firstName").as[String],
    (json \ "lastName").as[String],
    (json \ "email").as[Option[String]]
  )

  def writes(user: User) = JsObject(Seq(
    "id" -> JsNumber(user.id),
    "firstName" -> JsString(user.firstName),
    "lastName" -> JsString(user.lastName),
    "email" -> Json.toJson(user.email)
  ))
}

And you'd use it like this:

scala> User(1L, "Some", "Person", Some("s.p@example.com"))
res0: User = User(1,Some,Person,Some(s.p@example.com))

scala> Json.toJson(res0)
res1: play.api.libs.json.JsValue = {"id":1,"firstName":"Some","lastName":"Person","email":"s.p@example.com"}

scala> res1.as[User]
res2: User = User(1,Some,Person,Some(s.p@example.com))

See the documentation for more information.

edited Jul 05 '22 at 14:03

botchniaque

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answered Aug 16 '12 at 02:39

Travis Brown

138,631
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Fantastic, thanks! And what if I wanted a Seq[User] as Json? :) – LuxuryMode Aug 16 '12 at 15:25
Play comes with an instance for `Seq`, so you can just use `Json.toJson(users).as[Seq[User]]`. – Travis Brown Aug 16 '12 at 19:30
Using Play's `JsNumber` with Mongo, I get a serialization error: `[error] play - Cannot invoke the action, eventually got an error: java.lang.IllegalArgumentException: can't serialize class scala.math.BigDecimal` – Kevin Meredith Sep 18 '13 at 19:42
Doesn't work anymore, `def reads(user: User) = JsResult[…]`, it cannot be `def reads(user: User) = User(…)` – Ashesh Sep 06 '14 at 15:42
This is out of date for Play 2.4, can someone provide an update? – Ethan Mick Sep 02 '15 at 14:37

score 9 · Answer 2 · answered Apr 04 '14 at 07:22

9

Thanks to the fact User is a case class you could also do something like this:

implicit val userImplicitWrites = Json.writes[User]
val jsUserValue = Json.toJson(userObject)

without writing your own Format[User]. You could do the same with reads:

implicit val userImplicitReads = Json.reads[User]

I haven't found it in the docs, here is the link to the api: http://www.playframework.com/documentation/2.2.x/api/scala/index.html#play.api.libs.json.Json$

answered Apr 04 '14 at 07:22

Paweł Kozikowski

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Just for completeness - without using implicits: `Json.reads[User].reads(myJson).get` – User Jun 29 '15 at 09:39
1

This one should now be marked as the answer. Here's the link for the updated doc: https://www.playframework.com/documentation/2.5.x/ScalaJsonAutomated – Gustavo Maloste Oct 19 '16 at 18:12

serializing objects to json with play.api.libs.json

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