Java - Factura Electronica con EFACT - PERU

private static String getResourceCredentials(String userName, String password) {

    String content = "grant_type=password&username=" + userName + "&password=" + password;

    BufferedReader reader = null;

    HttpsURLConnection connection = null;

    String returnValue = "";

    try {

        URL url = new URL(tokenUrl);

        connection = (HttpsURLConnection) url.openConnection();

        connection.setRequestMethod("POST");

        connection.setDoOutput(true);

        connection.setRequestProperty("Authorization", "Basic " + authentication);

        connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

        connection.setRequestProperty("Accept", "application/json");

        PrintStream os = new PrintStream(connection.getOutputStream());

        os.print(content);

        os.close();

        reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));

        String line = null;

        StringWriter out = new StringWriter(connection.getContentLength() > 0 ? connection.getContentLength() : 2048);

        while ((line = reader.readLine()) != null) {

            out.append(line);

        }

        String response = out.toString();

        Matcher matcher = pat.matcher(response);

        if (matcher.matches() && matcher.groupCount() > 0) {

            returnValue = matcher.group(1);

        }

    } catch (Exception e) {

        System.out.println("Error : " + e.getMessage());

    } finally {

        if (reader != null) {

            try {

                reader.close();

            } catch (IOException e) {

            }

        }

        connection.disconnect();

    }

    return returnValue;

}