5

这是我的任务。给定一对纬度和经度，我想从 Google Places API 获取 JSON。下面的函数 reverseGeoCoding 返回字符串 JSON。

public String reverseGeoCoding(String lat, String lng) {
    latitude = lat;
    longitude = lng;
    String json = new String();
    String url = new String();

    URL googleAPI;
    try {
        url = URL + "location=" + latitude + "," + longitude + "&" + "radius=" + radius + "&" + "language=" + language + "&" + "sensor=false" + "&" + "key=" + APIKey;

        googleAPI = new URL(url);
        Log.d("TEST", googleAPI.toString());
        URLConnection gc = (URLConnection) googleAPI.openConnection();
        Log.d("TEST", gc.toString());

        InputStream is = gc.getInputStream();
        Log.d("TEST", "InputStream created");
        BufferedReader in = new BufferedReader(new InputStreamReader(is));
        Log.d("TEST", "reader created");
        String inputLine;
        while ((inputLine = in.readLine()) != null) {
            json = json + inputLine + "\n";
            Log.d("TEST", inputLine);
        }

        in.close();

    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    return json;
}

但是，getInputStream() 不起作用。我已经检查了网络浏览器上的 url 请求，它工作正常（返回 JSON 文档）。

错误消息如下。（为什么第 17 行和第 18 行会产生错误）

1. 12-11 00:46:02.862: W/System.err(12953): android.os.NetworkOnMainThreadException
2. 12-11 00:46:02.872: W/System.err(12953):     at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1084)
3. 12-11 00:46:02.872: W/System.err(12953):     at java.net.InetAddress.lookupHostByName(InetAddress.java:391)
4. 12-11 00:46:02.872: W/System.err(12953):     at java.net.InetAddress.getAllByNameImpl(InetAddress.java:242)
5. 12-11 00:46:02.872: W/System.err(12953):     at java.net.InetAddress.getAllByName(InetAddress.java:220)
6. 12-11 00:46:02.872: W/System.err(12953):     at libcore.net.http.HttpConnection.<init>(HttpConnection.java:71)
7. 12-11 00:46:02.872: W/System.err(12953):     at libcore.net.http.HttpConnection.<init>(HttpConnection.java:50)
8. 12-11 00:46:02.882: W/System.err(12953):     at libcore.net.http.HttpConnection$Address.connect(HttpConnection.java:351)
9. 12-11 00:46:02.882: W/System.err(12953):     at libcore.net.http.HttpConnectionPool.get(HttpConnectionPool.java:86)
10. 12-11 00:46:02.882: W/System.err(12953):    at libcore.net.http.HttpConnection.connect(HttpConnection.java:128)
11. 12-11 00:46:02.882: W/System.err(12953):    at libcore.net.http.HttpEngine.openSocketConnection(HttpEngine.java:308)
12. 12-11 00:46:02.882: W/System.err(12953):    at libcore.net.http.HttpsURLConnectionImpl$HttpsEngine.makeSslConnection(HttpsURLConnectionImpl.java:460)
13. 12-11 00:46:02.882: W/System.err(12953):    at libcore.net.http.HttpsURLConnectionImpl$HttpsEngine.connect(HttpsURLConnectionImpl.java:432)
14. 12-11 00:46:02.882: W/System.err(12953):    at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:282)
15. 12-11 00:46:02.882: W/System.err(12953):    at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:232)
16. 12-11 00:46:02.882: W/System.err(12953):    at libcore.net.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:273)
17. 12-11 00:46:02.882: W/System.err(12953):    at libcore.net.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:168)
18. 12-11 00:46:02.894: W/System.err(12953):    at libcore.net.http.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:270)
19. 12-11 00:46:02.894: W/System.err(12953):    at locationpredict.POIList.reverseGeoCoding(POIList.java:55)
20. 12-11 00:46:02.894: W/System.err(12953):    at locationpredict.TestMain$1.onClick(TestMain.java:62)
4

3 回答 3

5

由于人们在主线程上使用繁重的网络操作导致应用程序无响应，因此添加了此新功能以防止人们这样做。
您应该使用 AsyncTask 或服务来执行此操作。

        private class GetJsonTask extends AsyncTask<String, Void, String>{


            @Override
            protected String doInBackground(String... params) {
        try {
            latitude = params[0];
             longitude = params[1];
             String json = new String();
             String url = new String();
             URL googleAPI;


            url = URL + "location=" + latitude + "," + longitude + "&" + "radius=" + radius + "&" + "language=" + language + "&" + "sensor=false" + "&" + "key=" + APIKey;

            googleAPI = new URL(url);
            Log.d("TEST", googleAPI.toString());
            URLConnection gc = (URLConnection) googleAPI.openConnection();
            Log.d("TEST", gc.toString());

            InputStream is = gc.getInputStream();
            Log.d("TEST", "InputStream created");
            BufferedReader in = new BufferedReader(new InputStreamReader(is));
            Log.d("TEST", "reader created");
            String inputLine;
            while ((inputLine = in.readLine()) != null) {
                json = json + inputLine + "\n";
                Log.d("TEST", inputLine);
            }

            in.close();

        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
         return json;
    }

    @Override
        protected void onPostExecute(String result) {
            parseJson(result); // json should be stored in the result
        }
  }

private void parseJson(String json){
     JSONObject obj = new JSONObject(json);
....

}

像这样称呼它：

String[] data = new String[2];
data[0] = lat;
data[1] = long;
new GetJsonTask().execute(data);

或者你可以通过在调用方法之前在你的 onCreate() 方法中添加以下代码来绕过它，但我不推荐这种方法。只需将其用于测试。

   if( Build.VERSION.SDK_INT >= 9){
            StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
            StrictMode.setThreadPolicy(policy);
    }
于 2012-12-11T01:25:40.753 回答
2

> android.os.NetworkOnMainThreadException ：

当应用程序尝试在其主线程上执行网络操作时引发的异常。

使用AsyncTask来避免这个错误。并将所有与网络相关的任务放在doInBackgroundAsyncTask 的方法中

于 2012-12-11T01:14:15.720 回答
0

正如其他答案所建议的那样，使用异步任务。还推荐使用gson将对象转换为/从 json 字符串！

于 2012-12-11T02:25:42.363 回答