How to Keep Uploaded Files When Redeploying a Dockerized Spring Boot App?

Hey everyone! I'm new to DevOps and Docker, and I'm having a bit of trouble. I'm working on containerizing an open-source Spring Boot project (Vireo) using Maven. The build runs smoothly, but there's a major catch: any files uploaded by users get stored in the JAR directory. This means that whenever I rebuild the image or create a new container, all the uploaded files disappear.

The relevant section in my `application.yml` looks like this:

```
app:
url: http://localhost:${server.port}

# comment says: 'override assets.uri with -Dassets.uri=file:/var/vireo/'
assets.uri: ${assets.uri}

public.folder: public
document.folder: private
```

My current run command is:

```
docker run -d --name vireo -p 9000:9000 your-image:latest
```

What I suspect is happening is that since `assets.uri` isn't explicitly set, Spring defaults to a relative path inside the fat JAR (`/app.jar!/WEB-INF/classes/private/...`). When the container stops or the image is rebuilt, that path is lost, which explains the missing uploads.

I've tried a couple of things:
1. Changing `document.folder` to an absolute path (`/vireo/uploads`), but uploads still go into the JAR unless I add `file:/`.
2. Adding `VOLUME /var/vireo` to my Dockerfile, which creates the folder but Spring still writes to the JAR.

Here are my questions:
1. Is using `assets.uri=file:/var/vireo/` the right approach, or should I set it at build-time with `-Dassets.uri`?
2. Are there any particular issues with missing trailing slashes or the `file:` scheme that I should be aware of?
3. For anyone who's deployed Vireo or similar Spring Boot apps, did you find it better to handle uploads with a named Docker volume instead of a bind mount? What are the pros and cons?

Thanks a bunch for your help! 🙏