Play 2.1 Scala JSON parsing harder than Jerkson? - json

Question

With Jerkson, I was able to parse a String containing a JSON array, like this:
com.codahale.jerkson.Json.parse[Array[Credentials]](contents)
where contents was a String containing the following:
[{"awsAccountName":"mslinn","accessKey":"blahblah","secretKey":"blahblah"}]
... and I would get the array of Credentials.
(Brief diversion) I tried to do something similar using the new JSON parser for Play 2.1 and Scala using different data. For a simple parse, the following works fine. A case class (S3File) defines the unapply method necessary for this to work:
case class S3File(accountName: String,
bucketName: String,
endpoint: String = ".s3.amazonaws.com")
implicit val s3FileFormat = Json.format[S3File]
val jsValue = Json.parse(stringContainingJson)
Json.fromJson(jsValue).get
Let's reconsider the original string called contents containing JSON. As with all collections, an array of objects has no unapply method. That means the technique I showed in the the diversion above won't work. I tried to create a throwaway case class for this purpose:
case class ArrayCreds(payload: Array[Credentials])
implicit val credsFormat = Json.format[ArrayCreds]
val jsValue = Json.parse(contents)
val credArray = Json.fromJson(jsValue).get.payload
... unfortunately, this fails:
No unapply function found
[error] implicit val credsFormat = Json.format[ArrayCreds]
[error] ^
[error]
/blah.scala:177: diverging implicit expansion for type play.api.libs.json.Reads[T]
[error] starting with method ArrayReads in trait DefaultReads
[error] val credArray = Json.fromJson(jsValue).get
[error] ^
Is there a simple way of parsing an array of JSON using Play 2.1's new JSON parser? I expect the throwaway case class is the wrong approach, and the implicit will need to be instead:
implicit val credsFormat = Json.format[Credentials]
But I don't understand how to write the rest of the deserialization in a simple manner. All of the code examples I have seen are rather verbose, which seems contrary to the spirit of Scala. The ideal incantation would be as simple as Jerkson's incantation.
Thanks,
Mike

Answer 1

I think this is what you're looking for:
scala> import play.api.libs.json._
import play.api.libs.json._
scala> case class Credentials(awsAccountName: String, accessKey: String, secretKey: String)
defined class Credentials
scala> implicit val credentialsFmt = Json.format[Credentials]
credentialsFmt: play.api.libs.json.OFormat[Credentials] = play.api.libs.json.OFormat$$anon$1#1da9be95
scala> val js = """[{"awsAccountName":"mslinn","accessKey":"blahblah","secretKey":"blahblah"}]"""
js: String = [{"awsAccountName":"mslinn","accessKey":"blahblah","secretKey":"blahblah"}]
scala> Json.fromJson[Seq[Credentials]](Json.parse(js))
res3: play.api.libs.json.JsResult[Seq[Credentials]] = JsSuccess(List(Credentials(mslinn,blahblah,blahblah)),)
HTH,
Julien