Dropbox v2. Чтение каталога

private static final String APP_KEY = "ly2h44xro59e4sg";
    private static final String APP_SECRET = "krcj1lmdzpzm4sl";
    private static final String token = "EKpeC3qgzRAAAAAAAAAAE5K0YPRWz2OyELi-H1TgKfD9z_Jnw7rgKc-RQ9pBT9n9";
 
    mDbxAcctMgr = DbxAccountManager.getInstance(getApplicationContext(), APP_KEY, APP_SECRET);
    listFolder("");
 
    public void listFolder(String foldername) throws Exception {
 
        try {
            URL url = new URL("https://api.dropboxapi.com/2/files/list_folder");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            String parameters = "{\"path\": \"" + foldername + "\",\"recursive\": false,\"include_media_info\": false,\"include_deleted\": false,\"include_has_explicit_shared_members\": false}";
 
            conn.setRequestProperty("Accept", "application/json");
            conn.addRequestProperty("Authorization", token);
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Content-Type", "application/json");
 
            conn.setDoOutput(true);
            DataOutputStream writer = new DataOutputStream(conn.getOutputStream());
            writer.writeBytes(parameters);
            writer.flush();
            if (writer != null)
                writer.close();
 
            if (conn.getResponseCode() != 200) {
                System.out.println(conn.getResponseMessage());
                throw new RuntimeException("Failed : HTTP error code : "
                        + conn.getResponseCode());
            }
            BufferedReader br = new BufferedReader(new InputStreamReader(
                    (conn.getInputStream())));
            String output;
            System.out.println("Output from Server .... \n");
            while ((output = br.readLine()) != null) {
                System.out.println(output);
            }
            conn.disconnect();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

DataOutputStream writer = new DataOutputStream(conn.getOutputStream());