If you use NAT network configuration, the only way to access services inside the VM is to create a port forwarding. You can read more about that here.
In order to do that in VirtualBox, right click on the VM > Settings > Network > Advanced and click on Port Forwarding, and create a forwarding rule like the following one:
After that you can access your application at port 8080.
In any case, it would be great if you could debug your issue using Bridge adapter. For that, could you run these commands?
sudo /etc/init.d/networking force-reload
ip route get 1