Java從URL NullPointerException解析JSON

Question

我正在嘗試從以下API解析JSON： https ： //opentdb.com/api.php？amount = 1

但是當我試圖獲取問題值時，我收到以下錯誤：

Exception in thread "main" java.lang.NullPointerException

我用這個代碼：

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

}

希望有人能告訴我我做錯了什么。

提前致謝！

Answer 1

當我看到你試圖解釋的JSON時，我得到：

{
    "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"]
        }
    ]
}

此JSON不包含根成員"question" 。 這使得rootobj.get("question")返回null ，因此在其上調用getAsString會拋出NullPointerException 。

因此，不必使用rootobj.get("question") ，而是必須遍歷層次結構： "results" - >第一個數組成員 - > "question" ：

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

Answer 2

JSON沒有直接的“問題”字段。 call question = rootobj.get("result").get(0).get("question").getAsString(); 代替

Answer 3

試試這個吧

question = rootobj.getAsJsonArray（“results”）。get（0）.getAsJsonObject（）。get（“question”）。getAsString（）;