如何在Play中读取带有转义引号的JSON字符串

Question

I'm receiving some JSON from a server:

"payload":"{\"action\":\"schedule\"}"

For why I am getting this odd looking JSON see this question . I've written some code to parse this bit of the object:

  implicit val botPayloadReads: Reads[BotPayload] = (
    (JsPath \ """\"action\"""").read[String] and
      (JsPath \ """\"returnToAction"""").readNullable[String]
    )(BotPayload.apply _)

But I am getting an error:

List((/entry(0)/messaging(0)/postback/payload/\"action\",List(ValidationError(List(error.path.missing),WrappedArray()))))

Which is a little weird because the path \\"action\\" is exactly what we are looking for.

Answer 1

The reason those quotes are escaped is that the "payload" key actually has the String type, so it contains a string representation of an object. This is a very weird for a server to return, really. You will essentially need to re-parse the contents of payload 's value, or pre-process the JSON. This can all be done with Play's JSON API, though.

import play.api.data.validation.ValidationError
import play.api.libs.json._
import scala.util.{ Success, Try }

case class BotPayload(action: String, returnToAction: Option[String])

object BotPayload {

  val payloadReads = Json.reads[BotPayload]

  implicit val reads: Reads[BotPayload] = Reads.StringReads
    .map(s => Try(Json.parse(s)))
    .collect(ValidationError("Cound not parse content of payload")) {
      case Success(js) => js
    }
    .andThen(payloadReads)

}

scala> val js = Json.parse(""" {"payload":"{\"action\":\"schedule\"}"} """)
js: play.api.libs.json.JsValue = {"payload":"{\"action\":\"schedule\"}"}

scala> (js \ "payload").validate[BotPayload]
res0: play.api.libs.json.JsResult[BotPayload] = JsSuccess(BotPayload(schedule,None),)