[Ljava.lang.Object; error when using JSON arrays

I’m trying to send an array of elements as an argument (e.g. [String!]!) but I keep getting the following error: Variable '$temp' expected value of type '[String!]!' but got: [Ljava.lang.Object;@1232fa01. Reason: [at index #0] String value expected

This happens for any type (String, Int, Boolean, etc.) that attempts to use an array.

I’ve over simplified my setup to test this issue and even this very basic example doesn’t work for me (it’s missing a couple of pieces for simplicity, don’t worry about them… this works when not using an array):

val tempArg = Argument("temp", ListInputType(StringType))

val queryFields: List[Field[SangriaCtx, Unit]] = fields(
    Field("temp", OptionType(SomeObjectType),
      description = Some("Returns some object"),
      arguments = tempArg :: Nil,
      resolve = c => {
        // do anything that returns SomeObjectType..
      })

Query:

query temp($temp: [String!]!) {
  temp(temp: $temp) {
    name
  }
}

{
  "temp": [] // or ["word"], for example
}

Strangely (?) sending a string will cast it to a Vector with length of 1…

Please let me know if I’m doing something wrong… Thanks, Elad

[elad-stern]

OK, so this has been an incredibly specific issue that probably wouldn’t concern most people but it was eventually resolved. The root cause was indeed Finatra server. Finatra uses Jackson for JSON parsing and they encountered a performance issue you can read about here. They resolved it by opting to work with java objects instead of scala ones, but allowed an optional flag DeserializationFeature.USE_JAVA_ARRAY_FOR_JSON_ARRAY to be turned off in case it causes any issues - which it did for us.

Anyway, long story short, we deactivated this feature and everything now works as expected. Thanks!

[OlegIlyenko]

Alternatively, you can also write a custom InputUnmarshaller for this finatra-specific JSON format represented with Map[String, Any]. Though my first suggestion is probably a bit simpler to implement and use