How to change http to https on ubuntu running tomcat in .Jar?

Tomcat supports SSL but it can be tricky to setup. An easier solution is to stand up a web server or reverse proxy, terminate SSL there, and proxy the now insecure request to tomcat as an upstream. Its quite common to install the web server or reverse proxy on the same machine as tomcat depending on your needs.

A common choice for this is is nginx. Nginx provides a tomcat specific deployment guide Here.

The basic gist is:

1. Generate your certs
2. Configure nginx to proxy to tomcat as an upstream
3. Configure nginx to listen on port 443 using your generated certs for the TLS handshake

Just remember not to bind your tomcat server to port 8080 on a public interface or users will be able to reach it without the secure channel.