Java program without forward port in router

Question

I made application with java using socket. My computer is the server and my phone(android ) is the client. Only what i trying to do is to forward String from phone to client PC.

Everything works fine when i configure my router and open the port i using. i don't want every time when costumer will install my application will need to open port in the router.

I thought about using remote server that will run my server code. but i didn't find server that can do that . i don't want to make my pc a server for all costumers.

How does all the chats companies do it without open port?

Answer 1

You must look into UPnP. This is what /most/ if not /all/ torrent clients use to allow foreign connections, without forwarding ports. How chat clients do it is a different scenario. They use hacks such as firewall hole-punching using UDP (with an external server) http://www.h-online.com/security/features/How-Skype-Co-get-round-firewalls-747197.html see this link for details on UDP hole punching.

Also see this article http://www.codeproject.com/Articles/13285/Using-UPnP-for-Programmatic-Port-Forwardings-and-N for usage of UPnP. But this is in C++, but I think you will understand.

EDIT: http://4thline.org/projects/cling/ I found this. I think it can help you.

Answer 2

You had to open port probably because of your routers firewall :). If you already opened let us say port 9090 then every client app (android phone) will be able to connect to it :). Of course if somebody wants to install server on their own pc they would problably forward some ports and disable some firewalls. If you want server with no special requriements lookup VPS'es. :)