Use RouterFunction or plain Controller for BasicErrorController instead of @Controller

[dsyer]

There are only a few endpoints and none of them is very complex. It would be nice to have an annotation (reflection) free implementation. Wouldn't make much difference to most Spring Boot apps in a regular JVM, but it has a bigger impact on native images (where @RequestMapping is expensive).

[philwebb]

I'm pretty sure we've faced some issues when we changed those classes in the past. They're public, and I think a few people override them to apply custom behavior. If we change things, we'll probably need to leave the old classes.

[dsyer]

That's fair. There's already a base class. We could (for instance) just shift the weight of the implementation into the base class and use it (or another thin subclass) as a Controller.