How can i get lifetime Access Token

there is my main code

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private static final int CAMERA_PERMISSION_REQUEST = 100;
    private static final String[] REQUIRED_CAMERA_PERMISSIONS = new String[]{Manifest.permission.CAMERA};

    private static final String DROPBOX_APP_KEY = "hc2p6uj44p9pyoc";
    private static final String DROPBOX_APP_SECRET = "i cannot show this";
    private static final String DROPBOX_REDIRECT_URI = "https://auth-finish";

    private String DROPBOX_ACCESS_TOKEN = null;
    private PreviewView previewView;
    private ImageCapture imageCapture;
    private TextView addressTextView;

    private ExecutorService cameraExecutor = Executors.newSingleThreadExecutor();
    private FusedLocationProviderClient fusedLocationProviderClient;
    private Geocoder geocoder;

    // Add latitude and longitude variables
    private double latitudeValue;
    private double longitudeValue;

    @Override
    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);

        // Log the received intent data for debugging
        Log.d("Dropbox", "Received new intent: " + intent);

        // Extract and log the data URI
        Uri data = intent.getData();
        Log.d("Dropbox", "Intent data URI: " + data);

        if (data != null && data.toString().startsWith(DROPBOX_REDIRECT_URI)) {
            // Authorization successful, extract the authorization code
            String code = data.getQueryParameter("code");

            // Log the authorization code for debugging
            Log.d("Dropbox", "Authorization Code: " + 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);

            // Log the request details
            Log.d("Dropbox", "POST Request URL: " + requestUrl);
            Log.d("Dropbox", "POST Request Body: " + urlParameters);

            // 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');
                }

                // Log the response
                Log.d("Dropbox", "POST Response: " + response.toString());

                return response.toString();
            }
        } catch (Exception e) {
            // Log any exceptions
            Log.e("Dropbox", "Error in HTTP request: " + e.getMessage());
            return null;
        }
    }
    private void handleDropboxAuthorizationCallback(Intent intent) {
        // Log the received intent for debugging
        Log.d("Dropbox", "Handling Dropbox Authorization Callback 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");

            // Log the authorization code for debugging
            Log.d("Dropbox", "Authorization Code: " + code);

            // Now, exchange the authorization code for an access token and refresh token
            exchangeAuthorizationCodeForTokens(code);
        } else {
            // Log a message if the intent data is unexpected
            Log.d("Dropbox", "Invalid Dropbox Authorization Callback Intent Data: " + data);
        }
    }

    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;

                    // Log the request details
                    Log.d("Dropbox", "Token Exchange Request URL: " + url);
                    Log.d("Dropbox", "Token Exchange Request Body: " + requestBody);

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

                    // Log the response
                    Log.d("Dropbox", "Token Exchange Response: " + jsonResponse);

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

                    // Log the obtained access token
                    Log.d("Dropbox", "Access Token Obtained: " + DROPBOX_ACCESS_TOKEN);

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

                } catch (Exception e) {
                    // Log any exceptions
                    Log.e("Dropbox", "Error in token exchange: " + e.getMessage());
                }
                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)) {
            FileMetadata metadata = client.files().uploadBuilder(remotePath)
                    .withMode(WriteMode.ADD)
                    .uploadAndFinish(in);

            runOnUiThread(() -> {
                Toast.makeText(MainActivity.this, "Photo uploaded to Dropbox", Toast.LENGTH_SHORT).show();
                // Log metadata information
                Log.d("Dropbox", "File uploaded. Metadata: " + metadata.toString());
            });
        }

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