Java 在 PC 上运行 ServerSocket

Question

A common problem for a common project: I'm trying to run a ServerSocket Java program on my local PC and connect to it from an Android client. As others have experienced, things go smoothly when the client connects to the local address (eg. 192.168.xxx.xxx). If I try to connect through the internet, nothing happens:

Now, here are the things I tried:

• Created inbound/outbound rules in Windows Firewall to allow traffic for the Server Port (3000)
• Used the public IP in the client socket (IP obtained here)
• Set up port forwarding on my router: inbound connection on port 3000 are redirected to the local IP of the server (eg. 192.1686.xxx.xxx again)
• Check that the IP address of the server is listening to the port 3000 using "netstat -anp tcp".
• Disabled any firewall on my router, just in case.

Still, there is no connection. Using this tool ( https://www.canyouseeme.org/ ) I triedd checking that the port was visible (with the server app running of course), but nothing, all I get is a time out.

I'm out of options, I was hoping someone could show me what I'm missing.

Thanks.

Answer 1

(1) Does your PC where your server runs on have a public IP? If you haven't applied for one and are running your code in a home or working environment, your computer only has a private IP. And considering the fact, your server and client connect well in the same LAN, the problem may be the IP.

(2)If you do have a public Ip, does your server listen on all IP address or just the LAN? Check the server bind IP is '0.0.0.0', and in ServerSocket constructor you can just set it to be null.