这应该可以解决问题

String JsonResponse = HttpHelper.connect(SERVER_URL);
JSONObject json=new JSONObject(JsonResponse);

private static String convertStreamToString(InputStream is) {
        /*
         * To convert the InputStream to String we use the BufferedReader.readLine()
         * method. We iterate until the BufferedReader return null which means
         * there's no more data to read. Each line will appended to a StringBuilder
         * and returned as String.
         */
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        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();
            }
        }
        return sb.toString();
    }
    public static String connect(String url)
    {
        HttpClient httpclient = new DefaultHttpClient();
        HttpGet httpget = new HttpGet(url); 
        HttpResponse response;
        try {
            response = httpclient.execute(httpget);
            //Log.i(TAG,response.getStatusLine().toString());
            HttpEntity entity = response.getEntity();
            if (entity != null) {
                InputStream instream = entity.getContent();
                String result= convertStreamToString(instream);
                instream.close();
                return result;
            }
        } catch (ClientProtocolException e) {
        } catch (IOException e) {
        }
        return null;
    }