如何获取服务器URL以生成哈希

Question

我试图在我的android应用中通过PayU接受付款，但是我没有服务器，因此我使用firebase来存储数据。从视频中

https://youtu.be/gnQ0IF3XniM

我设法从视频中提到的服务器集成了PayU支付网关。我从服务器生成哈希的代码如下：

   @Override
   protected String doInBackground(String... postParams) {

            String merchantHash = "";
            try {
                //TODO Below url is just for testing purpose, merchant needs to replace this with their server side hash generation url
                URL url = new URL("https://payu.herokuapp.com/get_hash");

                String postParam = postParams[0];

                byte[] postParamsByte = postParam.getBytes("UTF-8");

                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("POST");
                conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
                conn.setRequestProperty("Content-Length", String.valueOf(postParamsByte.length));
                conn.setDoOutput(true);
                conn.getOutputStream().write(postParamsByte);

                InputStream responseInputStream = conn.getInputStream();
                StringBuffer responseStringBuffer = new StringBuffer();
                byte[] byteContainer = new byte[1024];
                for (int i; (i = responseInputStream.read(byteContainer)) != -1; ) {
                    responseStringBuffer.append(new String(byteContainer, 0, i));
                }

                JSONObject response = new JSONObject(responseStringBuffer.toString());

                Iterator<String> payuHashIterator = response.keys();
                while (payuHashIterator.hasNext()) {
                    String key = payuHashIterator.next();
                    switch (key) {
                        /**
                         * This hash is mandatory and needs to be generated from merchant's server side
                         *
                         */
                        case "payment_hash":
                            merchantHash = response.getString(key);
                            break;
                        default:
                            break;
                    }
                }

            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (ProtocolException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (JSONException e) {
                e.printStackTrace();
            }
            return merchantHash;
        }