A literal IP address or host name that can be resolved to an IP address. If not specified, defaults to 0.0.0.0.

Note about 0.0.0.0 While listening 0.0.0.0 works on all platforms, the browsers on Windows don't work with the address 0.0.0.0. You should show the message like server running on localhost:8080 instead of server running on 0.0.0.0:8080 if your program supports Windows.

The port to listen on.