Question

This is my code:

import play.api.mvc._
import play.api.libs.json._
import play.api.libs.json.Json._
import play.api.libs.json.Writes._

class BaseController extends Controller with Secured with DefaultWrites {

  private implicit def str2json(str: String) = new {
    def asSuccessJson = toJson(Map("success" -> true, "message" -> str)) // (*)
    def asFailedJson = toJson(Map("success" -> false, "message" -> str)) // (*)
  }

}

But it can’t be compiled on two (*) lines. The error message is:

Multiple markers at this line
- No Json deserializer found for type scala.collection.immutable.Map[java.lang.String,Any]. Try 
 to implement an implicit Writes or Format for this type.
- not enough arguments for method toJson: (implicit tjs: 
     play.api.libs.json.Writes[scala.collection.immutable.Map[java.lang.String,Any]])
     play.api.libs.json.JsValue.Unspecified value parameter tjs.

I have to write it as:

def asSuccessJson = toJson(Map("success" -> true.toString, "message" -> str))

Notice true.toString. It works but boring.

How to fix it?

Answer 1

It’s quite logical: you try to convert an heterogeneous map into a JsValue:

Map("success" -> true, "message" -> str) is a Map[String, Any].

There is no implicit writer able to convert a Map[String, Any] into a JsValue (and there can’t be any).

When you write Map("success" -> true.toString, "message" -> str), you create a Map[String, String] and there is a writer for this.

I would write:

def asSuccessJson = JsObject(Seq("success" -> JsBoolean(true), "message" -> JsString(str))) // (*)

BTW, the JSON API will certainly be “beautified” a bit in Play 2’s next releases…