题
我正在尝试从查询字符串中获取Google搜索的命中。
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"));
}
}
抛出以下例外:
Exception in thread "main" java.lang.NullPointerException
at odp.compling.Utils.googleHits(Utils.java:48)
at odp.compling.Utils.main(Utils.java:59)
我在做什么错误?我应该定义JSON返回的整个对象吗?鉴于我要做的就是获得一个价值,这似乎过多。
参考: 返回的JSON结构.
解决方案
看返回的JSON,看来您正在要求使用错误对象的估计resultScount成员。您正在要求hits.EstimatedResultScount,但是您需要hits.responsedata.cursor.stimatimatedResultscount。我对Gson并不熟悉,但我认为您应该做类似的事情:
return hits.get("responseData").get("cursor").get("estimatedResultsCount");
其他提示
我尝试了这一点,它使用了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;
}
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