Java parse JSON from URL NullPointerException

Question

I'm trying to parse the JSON from the following API: https://opentdb.com/api.php?amount=1

but when I'm trying to get the question value, I get the following error:

Exception in thread "main" java.lang.NullPointerException

I use this code:

public static void main(String[] args) throws IOException {
    String question;
    String sURL = "https://opentdb.com/api.php?amount=1"; //just a string

    // Connect to the URL using java's native library
    URL url = new URL(sURL);
    URLConnection request = 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.
    question = rootobj.get("question").getAsString(); //grab the question

}

Hope someone can tell me what I am doing wrong.

Thanks in advance!

what line is the NullPointerException? did you try to debug the program? — JavaSheriff
– JavaSheriff, Commented Jun 11, 2018 at 15:15
IT is for line 10: "question = rootobj.get("question").getAsString();" — kristoffer
– kristoffer, Commented Jun 11, 2018 at 15:19
so probably rootobj.get("question") is returning null, separate this line into 2 lines, — JavaSheriff
– JavaSheriff, Commented Jun 11, 2018 at 15:22

Waggili · Accepted Answer · 2018-06-11 15:33:18Z

7

When I look at the JSON you are trying to interpret, I get:

{
    "response_code": 0,
    "results":[
        {
            "category": "Entertainment: Board Games",
            "type": "multiple",
            "difficulty": "medium",
            "question": "Who is the main character in the VHS tape included in the board game Nightmare?",
            "correct_answer": "The Gatekeeper",
            "incorrect_answers":["The Kryptkeeper","The Monster","The Nightmare"]
        }
    ]
}

This JSON doesn't contain a root member "question". This makes rootobj.get("question") return null, and therefore calling getAsString on it throws the NullPointerException.

So instead of rootobj.get("question"), you would have to walk through the hierarchy: "results" -> first array member -> "question":

rootobj.getAsJsonArray("result").getAsJsonObject(0).get("question")

edited Jun 11, 2018 at 15:33

answered Jun 11, 2018 at 15:19

Waggili

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Comments

Daniel Przybylowski · Accepted Answer · 2018-06-11 15:29:45Z

2

Try this one

question = rootobj.getAsJsonArray("results").get(0).getAsJsonObject().get("question").getAsString();

answered Jun 11, 2018 at 15:29

Daniel Przybylowski

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Comments

Oz Molaim · Accepted Answer · 2018-06-11 15:19:15Z

2

The JSON has no direct "question" field. call question = rootobj.get("result").get(0).get("question").getAsString(); instead

answered Jun 11, 2018 at 15:19

Oz Molaim

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2 Comments

kristoffer Over a year ago

Hmm just tryed your snippet but now is says "Cannot resolve method 'get(int)'"

Oz Molaim Over a year ago

That is right, your are using Gson parser and it has diffrent syntax. Looks like @Daniel Przybylowski has the right syntax for you.

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