1. Don't use a random port for the Spring app. Use the default port and have Docker expose that as whatever port you like.
2. Don't use a random port for the Spring app. Specify it via an environment variable and have Docker provide that.

when you started an app, you can see at console I think. As I know docker use 8080 or 8081.

EDIT 1: Check this -> link

You can expose a port through your Dockerfile or use --expose and then publish it with the -P flag. This will bind the exposed port to your Docker host on a random port (verified by running docker container ls).

You can expose a port through your Dockerfile or use --expose and then publish it with the -p 80:80 flag. This will bind the exposed port to your Docker host on port 80, and it expects the exposed port is 80 too (adjust as necessary with HOST:CONTAINER).

You can ignore exposing anything and just use -p 80:80 in which case this doubles as both exposing AND publishing the port.