converting multiple json objects into scala objects

Question

How do I read multiple json objects from a request and convert them into my own custom object. For example, lets say we are retrieving a list of users with the following json:

{
  "users":[
    {
      "name": "Bob",
      "age": 31.0,
      "email": "[email protected]"
    },
    {
      "name": "Kiki",
      "age":  25.0,
      "email": null
    }
  ]
}

and my case class looks like the following

case class User(firstName: String, age: Double, email: String)

In this case the firstName value is differnt from the "name" json value. How do I get a Seq[User] from the given json file with the different names. I can't find any examples where someone is reading from a json file with multiple objects.

Thanks in advance.

Travis Brown · Accepted Answer · 2013-08-18 18:32:30Z

Play's type class-based JSON library provides reader and writer instances for Seq[A] for any A with the appropriate instances, so all you have to do is provide a reader instance for your user type and you get a reader for a collection of users for free.

We can start with the following case class (note that I've made the fact that the email address is optional explicit with Option):

case class User(firstName: String, age: Double, email: Option[String])

Next we define our reader. I'm using 2.1's combinators, but there are other (more verbose) options.

import play.api.libs.json._
import play.api.libs.functional.syntax._

implicit val userReads = (
  (__ \ 'name).read[String] and
  (__ \ 'age).read[Double] and
  (__ \ 'email).read[Option[String]]
)(User.apply _)

We can test it:

val userJson = """{
  "users": [
    { "name": "Bob",  "age": 31.0, "email": "[email protected]" },
    { "name": "Kiki", "age": 25.0, "email": null }
  ]
}"""

val users = (Json.parse(userJson) \ "users").as[Seq[User]]

And then:

scala> users foreach println
User(Bob,31.0,Some([email protected]))
User(Kiki,25.0,None)

As expected.

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