GSON JsonObject "Unsupported Operation Exception: null" getAsString - scala

Question

Running a Play! app with Scala. I'm doing a request where the response is expected to be a JSON string. When checking the debugger, the JsonElement returns OK with all information as expected. However, the problem is when I try to actually run methods on that JsonElement.
val json = WS.url("http://maps.googleapis.com/maps/api/geocode/json?callback=?&sensor=true&address=%s", startAddress+","+startCity+","+startProvince).get.getJson
val geocoder = json.getAsString
The only error I get back is Unsupported Operation Exception: null and I've tried this on getAsString and getAsJsonObject and getAsJsonPrimitive
Any idea why it's failing on all methods? Thanks.

Answer 1

I had a similar problem and I had to change jsonObject.getAsString() to jsonObject.toString();

Answer 2

Maybe your JsonElement is a JsonNull
What you could do is to first check that it isn't by using json.isJsonNull
Otherwise, try to get its String representation with json.toString

Answer 3

In my case I just needed to get the element as an empty string if it is null, so I wrote a function like this:
private String getNullAsEmptyString(JsonElement jsonElement) {
return jsonElement.isJsonNull() ? "" : jsonElement.getAsString();
}
So instead of
val geocoder = json.getAsString
You can just use this
val geocoder = getNullAsEmptyString(json);
It returns "" if the element is null and the actual string if it is not

Answer 4

To add to #Henry's answer. In the spirit of Kotlins "OrNull" Adding an extension function:
fun JsonElement.asStringOrNull(): String? {
return if (isJsonNull) null else asString
}

Answer 5

The class JsonElement will throw Unsupported Operation Exception for any getAs<Type> method, because it's an abstract class and makes sense that it is implemented in this way.
For some reason the class JsonObject, does not implement the getAs<Type> methods, so any call to one of these methods will throw an exception.
Calling the toString method on a JsonElement object, may solve your issue in certain circumstances, but isn't probably what you want because it returns the json representation as String (e.g. \"value\") in some cases.
I found out that also a JsonPrimitive class exists and it does implement the getAs<Type> methods. So probably the correct way to proceed is something like this:
String input = "{\"key1\":\"value1\",\"key2\":\"value2\"}";
JsonParser parser = new JsonParser();
JsonElement jsonTree = parser.parse(input);
if(jsonTree != null && jsonTree.isJsonObject()) {
JsonObject jsonObject = jsonTree.getAsJsonObject();
value = jsonObject.get("key1").getAsJsonPrimitive().getAsString()
}
PS. I removed all the nullability mgmt part. If you are coding in Java you probably want to manage this in a better way.
see GitHub source code for JsonElement:
https://github.com/google/gson/blob/master/gson/src/main/java/com/google/gson/JsonElement.java#L178