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I am fairly new to Java and I have tried looking up an answer for this for the last couple hours and so far I have nothing.

I am working with the Nobel Prize API for a project and I am getting an error when I try to convert to classes from the Json stream.

My code to read in the stream is this:

    Gson gson = new Gson();
    String sURL = "http://api.nobelprize.orgv1/laureate.json?bornCountry=Canada"; //just a string

    // Connect to the URL using java's native library
    URL url = new URL(sURL);
    HttpURLConnection request = (HttpURLConnection) url.openConnection();
    request.connect();

    // Convert to a JSON object to print data
    JsonParser jp = new JsonParser(); //from gson
    JsonElement root = jp.parse(new InputStreamReader((InputStream) request.getContent())); //Convert the input stream to a json element
    JsonObject rootobj = root.getAsJsonObject(); //May be an array, may be an object.
    LaureatesMain person = gson.fromJson(rootobj, LaureatesMain.class);
    System.out.println(person);
}

I am not checking for errors from the stream yet.

The json stream that I am looking at looks something like this:

{
    "laureates": [
        {
            "id": "140",
            // MORE STUFF
            "prizes": [
                {
                    "year": "1990",
                    // MORE STUFF
                    "affiliations": [
                        {
                            "name": "Stanford University",
                            "city": "Stanford, CA",
                            "country": "USA"
                        }
                    ]
                }
            ]
        }
    ]
}

I have a class for the laureates, prizes and affiliations and when it runs on Json like above I have no issue and it goes into the classes fine.

The problem I run into is if there is no entry in the affiliations then for some reason the API flips the {} to [] and gives me the following:

{
    "laureates": [
        {
            "id": "140",
            // MORE STUFF
            "prizes": [
                {
                    "year": "1990",
                    // MORE STUFF
                    "affiliations": [[]
                    ]
                }
            ]
        }
    ]
}

When I run on this one I get Expected BEGIN_OBJECT but was BEGIN_ARRAY at path 

$.laureates[###].prizes[0].affiliations[0]

I have tried looking at changing the GsonBuilder and tried to intercept the Json and change it before it goes into the Builder but so far nothing has worked for me.

I have no control over what I get from the API. I can deal with it being an empty class object or a null value in the final structure. This is a fairly early iteration of the project but so far this issue is stopping me from moving on to other things.

Thanks

Jey
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  • You won't be able to use `LaureatesMain person = gson.fromJson(rootobj, LaureatesMain.class);` If you dont have any control over the data format from the server. – JakeWilson801 Nov 15 '16 at 22:56
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    Sounds like a similar issues as this post: [Handling inconsistent data types in REST results (json) in Java](http://stackoverflow.com/questions/38714747/handling-inconsistent-data-types-in-rest-results-json-in-java). Have you taken a look at using a [`TypeAdapter`](https://google.github.io/gson/apidocs/com/google/gson/TypeAdapter.html)? – avojak Nov 15 '16 at 22:57
  • Even though you have no direct control, I'd file a bug report with the API provider. – dnault Nov 15 '16 at 23:21
  • @avojak Thanks, that was exactly what I was looking for. – Jey Nov 16 '16 at 01:05

1 Answers1

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Answering my own question so I can close it.

I ended up using a Type Adapter so thank you for directing me to that. Wasn't too hard once I knew what I was looking for.

Found really good information in the following java docs at :

https://google.github.io/gson/apidocs/com/google/gson/TypeAdapter.html

https://static.javadoc.io/com.google.code.gson/gson/2.6.2/com/google/gson/stream/JsonReader.html

Jey
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