android 中解析 json 字符串的问题， json 字符串是被压缩过的

我在做天气预报程序的时候遇到的问题，我通过 android 里面 HttpUrlConnection 连接到 http://wthrcdn.etouch.cn/weather_mini?city=北京这个网址，可以根据城市名查询天气信息，它返回的是一个 json 字符串，但是网上说这个网址返回的 json 字符串是被压缩过的，因此要自己解析，我用 GZIPInputStream 去解压缩，在 java 里面可以正常打印出结果，代码和结果如下：

new Thread(new Runnable() {

private boolean isGZip = true;

        @Override
        public void run() {
            HttpURLConnection connection = null;
            try {
                URL url = new URL("http://wthrcdn.etouch.cn/weather_mini?city=芜湖");
                //URL url = new URL("http://www.weather.com.cn/data/list3/city.xml");
                connection = (HttpURLConnection) url.openConnection();
                connection.setRequestMethod("GET");
                connection.setConnectTimeout(8000);
                connection.setReadTimeout(8000);
                String response = "";
                if (connection.getResponseCode() == 200) {// 判断请求码是否是200码，否则失败
                    InputStream is = connection.getInputStream(); // 获取输入流
                    System.out.println(connection.getContentEncoding());
                    if (isGZip ) {

                        //InflaterInputStream ilis = new InflaterInputStream(is);
                        GZIPInputStream in = new GZIPInputStream(is);
                        BufferedReader reader = new BufferedReader(
                                new InputStreamReader(in, "utf-8"));
                        String line = "";
                        while ((line = reader.readLine()) != null) {
                            response += line;
                        }
                    } else {
                        BufferedReader reader = new BufferedReader(
                                new InputStreamReader(is, "utf-8"));
                        String line = "";
                        while ((line = reader.readLine()) != null) {
                            response += line;
                        }
                    }
                }
                System.out.println(response);
            } catch (Exception e) {
            } finally {
                if (connection != null) {
                    connection.disconnect();
                }
            }
        }
    }).start();

运行结果是这样的：
gzip
{"desc":"OK","status":1000,"data":{"wendu":"26","ganmao":"相对于今天将会出现大幅度降温，空气湿度较大，易发生感冒，请注意适当增加衣服。","forecast":[{"fengxiang":"北风","fengli":"3-4级","high":"高温 28","type":"中雨","low":"低温 26","date":"9日星期天"},{"fengxiang":"北风","fengli":"微风级","high":"高温 29","type":"大雨","low":"低温 25","date":"10日星期一"},{"fengxiang":"北风","fengli":"微风级","high":"高温 28","type":"小雨","low":"低温 24","date":"11日星期二"},{"fengxiang":"西北风","fengli":"3-4级","high":"高温 27","type":"多云","low":"低温 23","date":"12日星期三"},{"fengxiang":"东风","fengli":"微风级","high":"高温 30","type":"多云","low":"低温 23","date":"13日星期四"}],"yesterday":{"fl":"4-5级","fx":"东风","high":"高温 32","type":"雷阵雨","low":"低温 27","date":"8日星期六"},"city":"芜湖"}}
可是，这完全相同的程序放在 android 里面执行时，我跟踪到 GZIPInputStream in = new GZIPInputStream(is); 这一句时，程序抛异常，直接走 catch 中的代码了，异常是 java.io.IOException: unknown format (magic number 227b)，搞了好久了都解决不了，求大神帮忙解决！不胜感激