Android 步骤 2 异步服务器请求

PayPal Developer Github 存储库中提供了此应用程序的完整示例代码（Android +节点服务器）。

此时已点击 PayPal 未来付款按钮，我们有来自 PayPal SDK 的身份验证代码和元数据 ID，我们需要将这些代码传递到我们的服务器以完成将来的付款流程。

在下面的后台流程中，我们正在做一些事情：

• 我们设置了服务器为 http://10.0.2.2:3000/fpstore 的 URI，它正在命中我们在 localhost 上运行的服务器的/fpstore 端点。
• 然后将设置将要发送的 JSON 对象，其中包含身份验证代码和元数据 ID。
• 然后建立连接。在成功请求（200/201 范围）的情况下，我们可以期待从服务器返回响应。我们读了那个回复，然后又回来了。
• 最后，我们设置了 onPostExecute(...) 方法来处理返回的服务器字符串。在这个例子的情况下，它只是记录。

public class ServerRequest extends AsyncTask<String, Void, String> {
    protected String doInBackground(String[] params){
        HttpURLConnection connection = null;
        try{
            //set connection to connect to /fpstore on localhost
            URL u = new URL("http://10.0.2.2:3000/fpstore");
            connection = (HttpURLConnection) u.openConnection();
            connection.setRequestMethod("POST");

            //set configuration details
            connection.setRequestProperty("Content-Type", "application/json");
            connection.setRequestProperty("Accept", "application/json");
            connection.setAllowUserInteraction(false);
            connection.setConnectTimeout(10000);
            connection.setReadTimeout(10000);

            //set server post data needed for obtaining access token
            String json = "{\"code\": \"" + params[0] + "\", \"metadataId\": \"" + params[1] + "\"}";
            Log.i("JSON string", json);

            //set content length and config details
            connection.setRequestProperty("Content-length", json.getBytes().length + "");
            connection.setDoInput(true);
            connection.setDoOutput(true);
            connection.setUseCaches(false);

            //send json as request body
            OutputStream outputStream = connection.getOutputStream();
            outputStream.write(json.getBytes("UTF-8"));
            outputStream.close();

            //connect to server
            connection.connect();

            //look for 200/201 status code for received data from server
            int status = connection.getResponseCode();
            switch (status){
                case 200:
                case 201:
                    //read in results sent from the server
                    BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                    StringBuilder sb = new StringBuilder();
                    String line;
                    while ((line = bufferedReader.readLine()) != null){
                        sb.append(line + "\n");
                    }
                    bufferedReader.close();

                    //return received string
                    return sb.toString();
            }

        } catch (MalformedURLException ex) {
            Log.e("HTTP Client Error", ex.toString());
        } catch (IOException ex) {
            Log.e("HTTP Client Error", ex.toString());
        } catch (Exception ex) {
            Log.e("HTTP Client Error", ex.toString());
        } finally {
            if (connection != null) {
                try{
                    connection.disconnect();
                } catch (Exception ex) {
                    Log.e("HTTP Client Error", ex.toString());
                }
            }
        }
        return null;
    }

    protected void onPostExecute(String message){
        //log values sent from the server - processed payment
        Log.i("HTTP Client", "Received Return: " + message);
    }
}