How can i get lifetime Access Token

this is my app code now look like
private static final String DROPBOX_APP_KEY = "secret";
private static final String DROPBOX_APP_SECRET = "secret";
private static final String DROPBOX_REDIRECT_URI = "decamera://auth-finish";

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    previewView = findViewById(R.id.previewView);
    ImageButton captureButton = findViewById(R.id.captureButton);
    ImageButton leftCornerButton = findViewById(R.id.leftCornerButton);
    addressTextView = findViewById(R.id.addressTextView);

    fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this);
    geocoder = new Geocoder(this, Locale.getDefault());

    captureButton.setOnClickListener(this);

    leftCornerButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            initiateDropboxAuthorization();
        }
    });

    addressTextView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            showEditAddressDialog();
        }
    });

    if (allPermissionsGranted()) {
        startCamera();
        getLastLocation();
    } else {
        ActivityCompat.requestPermissions(this, REQUIRED_CAMERA_PERMISSIONS, CAMERA_PERMISSION_REQUEST);
    }

    // Initialize Dropbox access token if available
    SharedPreferences prefs = getPreferences(Context.MODE_PRIVATE);
    DROPBOX_ACCESS_TOKEN = prefs.getString("dropboxAccessToken", null);

    // Check if the app was opened with a Dropbox authorization callback
    handleDropboxAuthorizationCallback(getIntent());
}

// Override onNewIntent to handle the Dropbox authorization callback
@Override
protected void onNewIntent(Intent intent) {
    super.onNewIntent(intent);
    handleDropboxAuthorizationCallback(intent);
}

private void handleDropboxAuthorizationCallback(Intent intent) {
    Uri data = intent.getData();
    if (data != null && data.toString().startsWith(DROPBOX_REDIRECT_URI)) {
        // Authorization successful, extract the authorization code
        String code = data.getQueryParameter("code");

        // Now, exchange the authorization code for an access token and refresh token
        exchangeAuthorizationCodeForTokens(code);
    }
}

private void initiateDropboxAuthorization() {
    // Construct the Dropbox authorization URL
    String authorizationUrl = "https://www.dropbox.com/oauth2/authorize" +
            "?client_id=" + DROPBOX_APP_KEY +
            "&response_type=code" +
            "&token_access_type=offline" +
            "&state=myState" +  // Replace with your own state
            "&redirect_uri=" + DROPBOX_REDIRECT_URI;

    // Open the authorization URL in a web browser or WebView
    Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(authorizationUrl));
    startActivity(browserIntent);
}
private String performPostRequest(String requestUrl, String urlParameters) {
    try {
        URL url = new URL(requestUrl);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("POST");
        connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
        connection.setRequestProperty("Content-Length", Integer.toString(urlParameters.getBytes().length));
        connection.setDoOutput(true);

        // Write the request body
        try (DataOutputStream wr = new DataOutputStream(connection.getOutputStream())) {
            wr.writeBytes(urlParameters);
            wr.flush();
        }

        // Get the response
        try (InputStream is = connection.getInputStream();
             BufferedReader rd = new BufferedReader(new InputStreamReader(is))) {
            StringBuilder response = new StringBuilder();
            String line;
            while ((line = rd.readLine()) != null) {
                response.append(line);
                response.append('\r');
            }
            return response.toString();
        }
    } catch (Exception e) {
        Log.e("HTTP", "Error in HTTP request: " + e.getMessage());
        return null;
    }
}
private void exchangeAuthorizationCodeForTokens(String code) {
    new AsyncTask<String, Void, Void>() {
        @Override
        protected Void doInBackground(String... params) {
            try {
                String url = "https://api.dropbox.com/oauth2/token";
                String requestBody = "code=" + params[0] +
                        "&grant_type=authorization_code" +
                        "&client_id=" + DROPBOX_APP_KEY +
                        "&client_secret=" + DROPBOX_APP_SECRET +
                        "&redirect_uri=" + DROPBOX_REDIRECT_URI;

                // Perform the POST request and obtain the JSON response
                String jsonResponse = performPostRequest(url, requestBody);

                // Parse the JSON response to extract access and refresh tokens
                JSONObject jsonObject = new JSONObject(jsonResponse);
                DROPBOX_ACCESS_TOKEN = jsonObject.getString("access_token");

                // Save the Dropbox access token
                SharedPreferences prefs = getPreferences(Context.MODE_PRIVATE);
                prefs.edit().putString("dropboxAccessToken", DROPBOX_ACCESS_TOKEN).apply();

            } catch (Exception e) {
                e.printStackTrace();
            }
            return null;
        }
    }.execute(code);
}

private void uploadToDropbox(File photoFile) {
    if (photoFile == null || !photoFile.exists()) {
        runOnUiThread(() -> Toast.makeText(MainActivity.this, "Error: Photo file does not exist", Toast.LENGTH_SHORT).show());
        return;
    }

    if (DROPBOX_ACCESS_TOKEN == null) {
        runOnUiThread(() -> Toast.makeText(MainActivity.this, "Error: Dropbox access token is null", Toast.LENGTH_SHORT).show());
        return;
    }

    DbxRequestConfig config = DbxRequestConfig.newBuilder("Decamera").build();
    DbxClientV2 client = new DbxClientV2(config, DROPBOX_ACCESS_TOKEN);

    try {
        String remotePath = "/Decamera/" + photoFile.getName();

        try (InputStream in = new FileInputStream(photoFile)) {
            client.files().uploadBuilder(remotePath)
                    .withMode(WriteMode.ADD)
                    .uploadAndFinish(in);

            runOnUiThread(() -> Toast.makeText(MainActivity.this, "Photo uploaded to Dropbox", Toast.LENGTH_SHORT).show());
        }

    } catch (Exception e) {
        e.printStackTrace();
        runOnUiThread(() -> Toast.makeText(MainActivity.this, "Error uploading to Dropbox: " + e.getMessage(), Toast.LENGTH_SHORT).show());
    }
}