communicate with computer that isn't on the same network

Question

I want to communicate between two computers that aren't on the same network, i tried to use sockets, but I only found tutorials and examples for communicating in the same network.
I tried to search on stackoverflow, but I had no clear idea of what to search for.
I want to send text two-way (chat).

-edit- The thing is, it is to me vague what I have to use or do, so I can't be much clearer then to say I want to send two way text (perhaps date) for a chatapp, just to learn from. -edit-

Answer 1

To communicate between two machines, they have to be on the same extended network. The only other option is to save data to external drives, e.g. USB drives, and you can attach to the second machine and up load.

You can use sockets to communicate with any other machine with an Internet connection, provided your firewall(s) and configured to allow the connection. The whole point of a firewall is to prevent unauthorised access. I suspect this is your real problem. If your firewalls prevent access, you should not be able to get around this using Java (google network hacking for alternatives ;)

Another option is to use a service such as email if the two computers cannot talk to each other directly (they still have to be connected to the same network) This is much more complex than using a direct connection but it can be done.

I suggest instead you configure your firewall(s) correctly and you will be able to use plain Sockets.

Answer 2

You have to get the external IPs (there are sites which while visiting give you this IP), and hope that the firewall allows communication. Typically one should use a port above 1000. There should be peer-to-peer libraries.

Another way is via SSH on one computer (JSch is one java library for SSH).

The easiest way is email exchange: the javax.mail API is compact but not the easiest. (Especially you could easily delete all mails, as I did once.)