使用OkHttpClient的android.os.NetworkOnMainThreadException

Question

我正在使用OkHttpClient来获取Gson。我正在使用这个Yahoo API网址：

http://query.yahooapis.com/v1/public/yql?q=select+*+from+yahoo.finance.historicaldata+where+symbol+%3D+%22YHOO%22+and+startDate+%3D+%222015-11-19%22+and+endDate+%3D+%222016-11-19%22&format=json&diagnostics=true&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys&callback=

之前有效，但有时无效。

   OkHttpClient mClient = new OkHttpClient();
    public String fetchStockHistory(String url) {
        try {
            Request request = new Request.Builder()
                    .url(url)
                    .build();

            Response response = mClient.newCall(request).execute();
            return response.body().string();
        } catch (Exception e){
            e.printStackTrace();
        }
        return null;
    }