今天遇到一个神奇的BUG，一个终端去下载一张图片，出现了504 Bad Gateway Timeout错误，把同样的url放到PC浏览器上又能正常打开，最后问题是解决了，但是具体原因还没搞清楚。

望有高人看到指点一下

出现问题的代码如下：

HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();        connection.setRequestMethod("GET");        if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {            InputStream is = connection.getInputStream();            BufferedInputStream bis = new BufferedInputStream(is);                        bis.mark(1024);            byte[] buffer = new byte[1024];            bis.read(buffer);            String orientation = parseOrientation(buffer);            // decode bitmap size            bis.reset();            bis.mark(bis.available());            Options options = new Options();            options.inJustDecodeBounds = true;            BitmapFactory.decodeStream(bis, null, options);            // decode scaled bitmap            bis.reset();            options.inSampleSize = calculateScaleSize(options.outWidth, options.outHeight);            options.inJustDecodeBounds = false;            Bitmap scaleBitmap = BitmapFactory.decodeStream(bis, null, options);            bis.close();            is.close();        }

经过多次尝试后，下面代码可以正常下载到图片：

HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();        connection.setRequestMethod("GET");        if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {            InputStream is = connection.getInputStream();            ByteArrayOutputStream baos = new ByteArrayOutputStream();            byte[] buffer = new byte[10240];            int length;            while ((length = is.read(buffer)) > -1) {                baos.write(buffer, 0, length);            }            baos.flush();            Log.d(TAG, "download finish: " + baos.size());            ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());            baos.close();            is.close();            bais.mark(1024);            buffer = new byte[1024];            bais.read(buffer);            String orientation = parseOrientation(buffer);            // decode bitmap size            bais.reset();            bais.mark(bais.available());            Options options = new Options();            options.inJustDecodeBounds = true;            BitmapFactory.decodeStream(bais, null, options);            // decode scaled bitmap            bais.reset();            options.inSampleSize = calculateScaleSize(options.outWidth, options.outHeight);            options.inJustDecodeBounds = false;            Bitmap scaleBitmap = BitmapFactory.decodeStream(bais, null, options);            bais.close();            is.close();        }

两种写法唯一的区别就是方法一是拿到InputStream后直接Decode，方法二是先把数据下载到内存然后Decode，为啥方法一就会出现“504 Bad Gateway Timeout”呢？