Jackson JSON parser can be a pain in the ass sometimes.
Like, bro, I don't want you to pollute my JSON when saving into Redis. Because now the frontend clients suddenly don't understand the schema because it's riddled with @class and type definitions everywhere.
You have to perform dark magic to get this thing to work automatically with Spring Boot caching.
I've had to implement my own custom serializer and deserializer after wasting who knows how many hours on this.
Shit like this is why I tend to roll my own implementation for many things at the slightest hint that a library isn't flexible.

Java's annotation system is just a plain disaster. I would avoid it as much as possible and it made my life better

there was this one time I just wanted like... a timer or something. I asked on stack overflow. I got 5 totally different replies of how to do it, not a single one worked. I then figured out a 6th way and it worked, posted it and marked it as the answer... and several people criticized it saying it's wrong for X and Y and etc reason 🤣, goddamnit lmao. it's the only one that would compile and actually function! IT'S JUST A TIMER!

I just needed a web service to do something regularly 😖

@jestdotty to be fair, timing is a platform feature where platform means something different depending on the order of magnitude of time. I would expect a mature ecosystem to offer at least 20 popular solutions under active development with different tradeoffs.