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我在从 Android 应用程序调用简单的 JSON Web 服务时遇到问题。.execute() 以 200-OK 状态成功完成，但是我无法读取任何 JSON 输出或文本。

作为记录，如果我 HttpPost 一个普通网页，比如 Google.com，我可以读取和解析所有标记。此外，我可以从设备的浏览器中调用完整的urlWithParams字符串，并在浏览器中看到 JSON 输出。这适用于设备的浏览器：

http://maps.googleapis.com/maps/api/distancematrix/json?origins=Seattle&destinations=San+Francisco&mode=bicycling&language=fr-FR&sensor=false

当代码运行时，阅读器总是空白并且 reader.readLine() 永远不会运行。返回一个空字符串。如果我将 URL 更改为 Google.com，它会起作用并返回 17,000 个字符。谢谢！

    protected String doInBackground(String... uri) {

    String responseString = null;   

    try {
                //String urlGoogle = "http://google.com";
                //String urlWithParams = "http://maps.googleapis.com/maps/api/distancematrix/json?origins=Seattle&destinations=San+Francisco&mode=bicycling&language=fr-FR&sensor=false";
                String urlOnly = "http://maps.googleapis.com/maps/api/distancematrix/json";
                HttpClient httpclient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(urlOnly);

                httpPost.setHeader("Accept", "application/json");
                httpPost.setHeader("Content-type", "application/json");

                List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
                nameValuePairs.add(new BasicNameValuePair("origins", "Seattle"));
                nameValuePairs.add(new BasicNameValuePair("destinations", "Cleveland"));
                nameValuePairs.add(new BasicNameValuePair("sensor", "false"));
                httpPost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

                HttpResponse response = httpclient.execute(httpPost);

                int status = response.getStatusLine().getStatusCode();

                HttpEntity entity = response.getEntity();
                InputStream is = entity.getContent();
                BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
                StringBuilder sb = new StringBuilder();

                String line = null;
                try {
                    while ((line = reader.readLine()) != null) {
                        sb.append((line + "\n"));
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    try {
                        is.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }

                responseString = sb.toString();
                }}
        catch (UnsupportedEncodingException e) {
            e.printStackTrace();
          } 
        catch (ClientProtocolException e) {
            e.printStackTrace();
        } 
        catch (IOException e) {
            e.printStackTrace();                
        } 

        return responseString;
    }
4

3 回答 3

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也许您应该测试其他 mime 类型而不是 application/json。

于 2013-11-06T13:41:25.123 回答
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1 - 检查您的清单文件是否具有 INTENET 权限。

2 - 使用此代码返回数据

  BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
try {
        String inputLine;
    while ((inputLine = reader.readLine()) != null) {
    responseString   += inputLine;
    }
} catch (IOException e) {
    e.printStackTrace();
} finally {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
   }
 }
于 2013-11-06T13:46:04.517 回答
0

解决了！调用 JSON 页面时返回空白是由于未定义代理设置。代理设置是在设备上设置的，但是根据这篇文章，HttpClient 不会继承它们。

添加以下行解决了我的问题。代码现在返回 JSON。

HttpHost proxy = new HttpHost("172.21.31.239", 8080);
httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY, proxy);
于 2013-11-07T00:29:38.097 回答