Comment by lmm

Spring boot specifically; regular Spring is relatively ok. I'm using it professionally at the moment. It's just impossible to find where anything is coming from or understand how your application is wired up, because everything magically appears based on what's on the classpath - it's like the COME FROM statement joke. Even just changing your dependency versions can suddenly radically change your application's behaviour (e.g. now it's suddenly running a webserver).