Converting your spring boot app to serve on HTTPS just requires few configuration to be added in application.yml:

server:
  ssl:
    key-store: C:\softwares\jdk-16\bin\demokeystore
    key-store-password: demopass
    key-alias: demokey 
  port: 8443

The above configuration is enough. Here is the explanation behind it:

https://fullstackdeveloper.guru/2021/04/23/how-to-convert-your-spring-boot-app-to-a-https-application/