private void login() {
        if (!validateAllInput()) {
            return;
        }

        try {
            String username = usernameField.getText();
            String password = String.valueOf(passwordField.getPassword());

            UserDao userDao = new UserDaoImpl();
            User user = userDao.findBy(username);
            boolean granted = isGranted(user, password, username);

            if (granted) {
                startMainActivity(user);
            }
        } catch (SQLException e) {
            e.printStackTrace();
            Throwable cause = e.getCause();
            if (cause instanceof ConnectException) {
                showWarning("Tidak dapat menghubungkan ke database server");
                return;
            }
            showWarning("Tidak bisa menghubungkan ke database \n\n"
                    + "Error : " + e.getMessage());
        }
    }

    private boolean isGranted(User user, String password, String username) {
        if (user == null) {
            showWarning("Tidak menemukan user dengan username : " + username);
            return false;
        }

        if (!user.getPassword().equals(password)) {
            showWarning("Password salah");
            return false;
        }

        return true;
    }

    private void startMainActivity(User user) {
        Session.getInstance().setUser(user);
        MainActivity frame = new MainActivity();
        frame.setVisible(true);
        frame.setLocationRelativeTo(null);
        dispose();
    }

    private boolean validateAllInput() {
        return validateUsername() && validatePassword();
    }

    private boolean validateUsername() {
        String username = usernameField.getText();

        if (username.isEmpty()) {
            showWarning("Username masih kosong");
            return false;
        }

        return true;
    }

    private boolean validatePassword() {
        String password = String.valueOf(passwordField.getPassword());

        if (password.isEmpty()) {
            showWarning("Password masih kosong");
            return false;
        }

        return true;
    }

    private void showWarning(String message) {
        JOptionPane.showMessageDialog(this, message, "Gagal",
                JOptionPane.ERROR_MESSAGE);
    }