Hmms, you might be right. I am not sure what's more expected from developers.
As a web developer I assume something like this in the war file:
/resources/db/changeSet.xml
/resources/db/photos/foto1.jpg

valueBlobFile = "/db/photos/foto1.jpg"
and not 
valueBlobFile = "/photos/foto1.jpg"

The biggest problem I see is how to correctly determine file size of the file in the JAR file. We have to find workaround for this. As @flyhard pointed, new File(urlResource.toURI()) throws exception (I didn't notice that, since Tomcat extracted my war file...).