Java：不正确地使用GSon？（空指针异常）

我试图从一串查询中获得谷歌搜索的点击率

public class Utils {

    public static int googleHits(String query) throws IOException {
        String googleAjax = "http://ajax.googleapis.com/ajax/services/search/web?v=1.0&q=";
        String json = stringOfUrl(googleAjax + query);
        JsonObject hits = new Gson().fromJson(json, JsonObject.class);

        return hits.get("estimatedResultCount").getAsInt();
    }

    public static String stringOfUrl(String addr) throws IOException {
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        URL url = new URL(addr);
        IOUtils.copy(url.openStream(), output);
        return output.toString();
    }

    public static void main(String[] args) throws URISyntaxException, IOException {
        System.out.println(googleHits("odp"));
    }

}

将引发以下异常：

Exception in thread "main" java.lang.NullPointerException
    at odp.compling.Utils.googleHits(Utils.java:48)
    at odp.compling.Utils.main(Utils.java:59)

我做错了什么？我应该为Json返回定义一个完整的对象吗？这似乎太过分了，因为我只想得到一个值

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仅供参考。

查看返回的JSON，似乎您要求的是错误对象的estimatedResultsCount成员。您正在请求hits.estimatedResultsCount，但需要hits.responseData.cursor.estimatedResultsCount。我对Gson不太熟悉，但我认为你应该做如下事情：

return hits.get("responseData").get("cursor").get("estimatedResultsCount");

---

我尝试了这个方法，它成功了，使用的是JSON而不是GSON

public static int googleHits(String query) throws IOException,
        JSONException {
    String googleAjax = "http://ajax.googleapis.com/ajax/services/search/web?v=1.0&q=";
    URL searchURL = new URL(googleAjax + query);
    URLConnection yc = searchURL.openConnection();
    BufferedReader in = new BufferedReader(new InputStreamReader(
            yc.getInputStream()));
    String jin = in.readLine();
    System.out.println(jin);

    JSONObject jso = new JSONObject(jin);
    JSONObject responseData = (JSONObject) jso.get("responseData");
    JSONObject cursor = (JSONObject) responseData.get("cursor");
    int count = cursor.getInt("estimatedResultCount");
    return count;
}