Well, to a degree it is done by a configuration file, it’s just written in the DSL of a big framework like spring. Like, most of the code is just declaratively

Well, to a degree it is done by a configuration file, it’s just written in the DSL of a big framework like spring. Like, most of the code is just declaratively specifying what should happen, not really the how. Add a few filter/mapping and you are ready.