Comment by cogman10

Yeah, it'll be unrelated to docker.

Uberjars are (typically) extracting all the classes from jar dependencies and combining them into a single jar. That's all gzip compression work.

Container layers are simply saved off filesystem modifications. If you use something like Jib to build your image, then the actual deployable should actually be a lot smaller than what you could do with an uber jar. That's because Jib will put your dependencies in one layer and your application jar in another. Assuming you work like most everyone, then that means the only thing that usually gets transferred is your application code. Dependencies only get sent if you change them or the base image.