Android 4.0 HttpUrlConnection的getInputStream()方法总是返回空的问题

 public String downTxt(String urlStr) {
         StringBuffer sBuffer = new StringBuffer();
         String line = null;
         BufferedReader bReader = null;
         try {
             URL url = new URL(urlStr);
             HttpURLConnection conn = (HttpURLConnection) url.openConnection();
             bReader = new BufferedReader(new InputStreamReader(
                     conn.getInputStream()));
             while ((line = bReader.readLine()) != null) {
                 sBuffer.append(line);
             }

         } catch (MalformedURLException e) {
             e.printStackTrace();
         } catch (IOException e) {
             e.printStackTrace();
         } finally {
             try {
                 bReader.close();
             } catch (IOException e) {
                 e.printStackTrace();
             }
         }

         return sBuffer.toString();
     }

 走到

 bReader = new BufferedReader(new InputStreamReader(
                     conn.getInputStream()));

 就会报空指针错误。为什么呢 ？

 ----------------

  改为 14以下版本。。。就OK。。。不行的话呢 再试试其他的sdk版本，总之就是这个地方的问题

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经测试，7，8，9三个版本是可以的，同时，去掉android:targetSdkVersion