如何在Play framework 2.3.x（Scala）中将case类转换为JSON？

Question

Anyone can show me how to convert case class class instances to JSON in Play framework (particularly Play v2.3.x) with Scala?

For example I have code like this:

case class Foo(name: String, address: String)

def index = Action {
      request => {
        val foo = Foo("John Derp", "Jem Street 21")  // I want to convert this object to JSON
        Ok(Json.toJson(foo))    // I got error at here
      }
}

The error message:

Cannot write an instance of com.fasterxml.jackson.data bind.JsonNode to HTTP response. Try to define a Writeable[com.fasterxml.jackson.databind.JsonNode]

UPDATE: I found out the above error is caused by wrong import of the Json class, it should be: import play.api.libs.json.Json . However I still got error on implicit problem below.

I have read this tutorial , but when I tried the implicit Writes[Foo] code:

  implicit val fooWrites: Writes[Foo] = (
        (JsPath \ "name").write[String] and
            (JsPath \ "address").write[String]
        )(unlift(Foo.unapply))

I got Can't resolve symbol and and Can't resolve symbol unlift error in Intellij. Also the tutorial's code looks complex just for the conversion of an object to JSON. I wonder if there is more simple way to do this?

Answer 1

You can get an Writes[Foo] instance by using Json.writes :

implicit val fooWrites = Json.writes[Foo]

Having this implicit in scope is all you need to convert Foo to JSON. See the documetnation here and here for more info about JSON reads/writes.

Answer 2

The second problem - Can't resolve symbol and - is an Intellij bug introduced in version 1.3 of the Scala plugin. In version 1.3.3 of the Scala plugin, there's now a workaround - set preference checkbox:

Languages & Frameworks > Scala > Core (default) tab > Use old implicit search algorithm