How to parse this JSON into a Map[String, User]? - json

Question

I want to go from the following JSON:
[
{
"name": "Cat",
"profile_image_url": "http://a0.twimg.com/profile_images/2284174872/7df3h38zabcvjylnyfe3_normal.png",
"location": "San Francisco, CA",
"id_str": "799346"
},
{
"name": "Dog",
"profile_image_url": "http://a0.twimg.com/profile_images/2284174758/v65oai7fxn47qv9nectx_normal.png",
"location": "San Francisco, CA",
"id_str": "783214"
}
]
to a Map[String, User], where the key is the name, and the User is the object that looks like this:
case class User(name: String, profileImage: String, id: String)
I'm using Play and Scala but am struggling to figure out how to do the JSON parsing.

Answer 1

First you can define an instance of the Reads type class for your type:
import play.api.libs.functional.syntax._
import play.api.libs.json._
implicit val userReads = (
(__ \ 'name).read[String] and
(__ \ 'profile_image_url).read[String] and
(__ \ 'id_str).read[String]
)(User.apply _)
And then you get a Reads[List[User]] instance for free that will decode your JSON:
Json.parse(jsonString).validate[List[User]]
That's not exactly what you want, but you can turn the list into a map pretty easily:
Json.parse(jsonString).validate[List[User]].map(_.map(u => u.name -> u).toMap)
And now you've got a JsResult[Map[String, User]].

Answer 2

Alternatively, maybe you can use argonaut, it provides more friendly api.
val json: String = """[
{
"name": "Cat",
"profile_image_url": "http://a0.twimg.com/profile_images/2284174872/7df3h38zabcvjylnyfe3_normal.png",
"location": "San Francisco, CA",
"id_str": "799346"
},
{
"name": "Dog",
"profile_image_url": "http://a0.twimg.com/profile_images/2284174758/v65oai7fxn47qv9nectx_normal.png",
"location": "San Francisco, CA",
"id_str": "783214"
}
]"""
import argonaut._, Argonaut._
case class User(name: String, url: String, location: String, idStr: String)
implicit def UserCodecJson =
casecodec4(User.apply, User.unapply)("name", "profile_image_url", "location", "id_str")
val result = json.decodeValidation[List[User]]
println(result) //Success(List(User(Cat,http://a0.twimg.com/profile ....
The good thing about this result is Scalaz Validation, because Validation is monad, so you can bind (flatmap) it with other Validation.

Answer 3

You can try this way:
1 Define you Case class with format:
case class User(name: String, profileImage: String, id: String) {
implicit val jsonFormat: Format[User] = Json.format[User]
}
2 parsing your json as List[User]
val jsonStr: String = ...
val users = Json.parse(jsonStr).as[List[User]]
3 group your List[User] to Map[String, User]
val whatYourWant:Map[String, User] = users.groupBy(_.name)