GSON with Scala - Unable to invoke no-args constructor for scala.collection.immutable.Map

Question

Here is a sample Scala object in which I want to deserialize a JSON String to a `Map of String -> String`. I use GSON 2.2.2 and Scala 2.10. ``` import com.google.gson.Gson import com.google.gson.reflect.TypeToken object MyTest { def main(args: Array[String]) { val gson = new Gson val jsonString = "{\"test1\": \"value-test1\",\"test2\":\"value-test2\"}" val mapType = new TypeToken[Map[String, String]] {}.getType val map = gson.fromJson(jsonString, mapType).asInstanceOf[Map[String, String]] } } ``` And that is the stack trace thrown in the line of `val map = ...`: ``` Exception in thread "main" java.lang.RuntimeException: Unable to invoke no-args constructor for scala.collection.immutable.Map<java.lang.String, java.lang.String>. Register an InstanceCreator with Gson for this type may fix this problem. at com.google.gson.internal.ConstructorConstructor$8.construct(ConstructorConstructor.java:167) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAda…

Accepted Answer

Oh, it is because `Map` does not have a constructor with no arguments, I can switch to `scala.collection.immutable.HashMap` then the error does not appear, but the `map` does not have the values, it is completely empty. It is only a `HashMap` with `serialVerionUID`, no more fields.

GSON with Scala - Unable to invoke no-args constructor for scala.collection.immutable.Map

Solution

Problem