Question

我正在尝试检索JSON对象并通过它解析，这样我就可以在地图上的2个点之间获取相应的LatLng对象。到目前为止，我已经实现了一个看起来像这样的测试类：

/**
 * Necessary imports
 */

public class DemoDirections extends AsyncTask<String, Void, Void > {
    ArrayList<LatLng> latLngs;
    JsonFactory JSON_FACTORY = new JsonFactory();
    JsonParser jParser;

    public DemoDirections() {
        //To access the Maps and Directions API for directions
    }

    protected Void doInBackground(String... src) {

        String urlString = "http://maps.googleapis.com/maps/api/directions/json?" +
                "origin=" + src[0] +"&destination="+ src[1] +"&sensor=false";
        Log.d("URL", urlString);
        HttpURLConnection urlConnection = null;
        URL url = null;

        try {

            url = new URL(urlString);
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.setDoOutput(true);
            urlConnection.setDoInput(true);
            urlConnection.connect();
            jParser = JSON_FACTORY.createJsonParser(urlConnection.getInputStream());
            String test = jParser.nextTextValue() != null ?  jParser.nextTextValue() : "its still null" ;
            Log.d("test string: ", test);

        } catch (Exception e) {
            e.printStackTrace();
        }

        return null;
    }

    protected void onPostExecute(String... src)
    {

    }
}

我只想将JSON打印为字符串，以确保在开始解析JSON输入之前我已正确接收到信息，但始终调用jParser.nextTextValue（）或jParser.textValue（）返回null，这使我认为我没有正确建立Google API服务。我只是想看看我缺少什么来检索JSON输入并解析它，以便我可以设置LatLng对象。

Answer 1

好像你的网址没有提供api密钥。示例API要求网址应如下所示：https://maps.googleapis.com/maps/api/geocode/json?address=1600+Amphitheatre+Parkway,+Mountain+View,+CA&key=API_KEY

示例工作代码：

String API_KEY = "YOUR_API_KEY_STRING";
String input = "1600+Amphitheatre+Parkway,+Mountain+View,+CA";

private static boolean getAddressResult(String input, StringBuilder jsonResults) {
    try {

        URL requestUrl = new URL("https://maps.googleapis.com/maps/api/geocode/json?address=" + input " + &key=" + API_KEY;
            );
        HttpURLConnection connection = (HttpURLConnection)requestUrl.openConnection();
        connection.setRequestMethod("GET");
        connection.connect();


        responseCode = connection.getResponseCode();
        if (responseCode == HttpURLConnection.HTTP_OK) {

            BufferedReader reader = null;

            InputStream inputStream = connection.getInputStream();
            StringBuffer buffer = new StringBuffer();
            if (inputStream == null) {
                // Nothing to do.
                return false;
            }
            reader = new BufferedReader(new InputStreamReader(inputStream));

            String line;
            while ((line = reader.readLine()) != null) {
                long elapsedTime = System.currentTimeMillis();
                if(elapsedTime-currentTime>=5000) {
                   return false;
                }
                buffer.append(line + "\n");
            }

            if (buffer.length() == 0) {
                return false;
            }

            Log.d("Test", buffer.toString());
            return buffer.toString();
        }
        else {
            Log.i(TAG, "Unsuccessful HTTP Response Code: " + responseCode);
            return false
        }
    } catch (MalformedURLException e) {
        Log.e(LOG_TAG, "Error processing Places API URL", e);
        return false;
    } catch (IOException e) {
        Log.e(LOG_TAG, "Error connecting to Places API", e);
        return false;
    } catch (Expcetion e) {
        return false;
    }
    return false;
}

请确保您必须在清单文件中设置正确的权限（例如INTERNET）。您还可以确保设备上的互联网实际已连接。

Answer 2

您是否尝试从'urlConnection.getInputStream（）'打印出数据？来自“http://maps.googleapis.com/maps/api/directions/json？”的回复数据应该是一个文本字符串（Json格式字符串），您可以读取它。

使用Google Maps API V2获取行车路线并检索JSON对象

2 个答案: