productFormatあるよ！

productFormatUsage.scala

scala> import play.api.libs.json._
import play.api.libs.json._

scala> import play.api.libs.json.Generic._
import play.api.libs.json.Generic._

scala> case class User(id: Long, name: String, age: Int)
defined class User

scala> implicit def userFormat: Format[User] = productFormat3("id", "name", "age")(User.apply)(User.unapply)
userFormat: play.api.libs.json.Format[User]

scala> Json.toJson(User(1, "peter", 20))
res0: play.api.libs.json.JsValue = {"id":1,"name":"peter","age":20}

scala> Json.stringify(Json.toJson(User(1, "peter", 20)))
res1: String = {"id":1,"name":"peter","age":20}