Programming

Spring combines combinations of environment variables, system properties, files, and classpath resources, and handles a variety of patterns (e.g.: aConfigOption could be configured by system property A_CONFIG_OPTION, aConfigOption, or several other possibilities), so tracking down where the configuration came from is not always easy. Sometimes you think you can just set a property, but it turns out another property triggers loading a resource that overrides yours. This would be fine if applications/libraries clearly documented how to configure them, but most say "config via spring, good luck lol".

And good luck if you are trying to use two different components both built on Spring, and they both rely on the dependency injector settings "db.url". Now you have to start playing games with dependency injector scopes.