Java 从 URL NullPointerException 解析 JSON

Question

我正在尝试从以下 API 解析 JSON: https://opentdb.com/api.php?amount=1

但是当我尝试获取问题值时，出现以下错误:

Exception in thread "main" java.lang.NullPointerException

我使用这个代码:

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

}

希望有人能告诉我我做错了什么。

提前致谢!

Answer 1

当我查看您尝试解释的 JSON 时，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 不包含根成员“question”。这使得 rootobj.get("question") 返回 null，因此对其调用 getAsString 会抛出 NullPointerException .

因此，您必须遍历层次结构，而不是 rootobj.get("question"):"results" -> 第一个数组成员 -> “问题”:

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