How to connect 2 computers on different networks using sockets.?

Question

Java

Whether who can prompt probably to connect 2 machines in different networks through external IP. Or only through the server on the hosting is possible. For example, I wrote a remote access program with a full set of operations with files, with uploading and downloading files from a remote machine, but it works only inside the local network. And I would like, for example, that being in China I could connect to a remote machine.
I only came up with a solution to connect through a proxy, but then all the data will go through someone's Hosting, and I'm scared to become something, what is the solution. This question is not designed for this program.
We need a principle of implementation, not a program.
All solutions that I found use the scheme. Client->Server->Client. Or like this Client->Server (receives a socket and binds it with another client.) As a result, a Client<->Client2 connection is obtained.
Is it possible to make a connection immediately Client<->Client2

Answer 1

It went a lot.
NAT will help you.
Only you are afraid of proxies. Aren't you afraid to open a listening port on the Internet? Be afraid! As soon as you go out into the world, they will immediately start breaking you - connections from left addresses, password guessing, etc. will begin. etc. Therefore, without serious software preparation, it is better not to put it on the Internet.
Organize VPN and expose your program inside VPN.

Answer 2

There are other solutions to control miners)
ps Why don't programs like teamweaver suit you?