通过 Internet 的 TCP 套接字连接

Question

I am doing a project for which connection between server and client is required. I did it by adding TCP sockets.

Here is the code fraction : Server:

    ServerSocket welcomeSocket = new ServerSocket(80);
    while(true)
    {
        Socket connectionSocket = welcomeSocket.accept();
        WorkerThread wt = new WorkerThread(connectionSocket, id);
        Thread t = new Thread(wt);
        t.start();
        workerThreadCount++;

    }

Client :

        Socket skt = new Socket("192.168.0.108", 80); // The IP address is from cmd->ipconfig/all-> IPv4 Address
        outToServer = new PrintWriter(skt.getOutputStream(), true);
        inFromServer = new BufferedReader(new InputStreamReader(skt.getInputStream()));

It all works when both ends are in same device/under same WiFi.But I don't understand what to do for creating connection over internet.

Please help with clear steps.

Answer 1

Here:

Socket skt = new Socket("192.168.0.108", 80);

That is local address. If you want to have a server that is reachable on the internet, then that server needs to have its global public IP address!

In other words: you have to make sure that the server can be reached from the internet somehow. For example by turning to some service provider that hosts servers that you can then equip with your code!

The whole purpose of 192.168 addresses is to be defined only in a local subnet.

Alternatively, you have to check if your ISP has a service where the ISP assigns an IP address to your connection, and that allows calls from the internet to go to your "place".

Meaning: when you want to receive phone calls, you need a phone that is connected to the phone net!

Answer 2

In order to connect to a socket over WAN, you must port forward that port to your local device. This can be done in your routers' settings.

192.168.0.108 --> That's your local IP-address.

This can be used on your local network without any requirements for port forwarding whatsoever. However, to use it over WAN, execute the following steps:

Step 1: Search for your routers' model number and port forwarding on Google on how-to forward port 80 to your local IP-address. Warning: use a static IP-address on your local device to prevent your IP from changing after a reboot.

Step 2: Go to a website like IP Chicken and find your external IP-address.

You can then connect to your socket using:

Socket skt = new Socket("[EXTERNALIP]", 80);

Please be noticed: unless you have a business network, your external IP-address will probably change from time to time.