In my company we're told to stop using global variables since our services are singleton and that's lead to problems however I gave manager my humble opinion that we should create an annotation that'll use ThreadLocal under-the-hood while initializing and will set/remove elements automatically however I couldn't convince him using that, I just wanna know whether the advice I gave was better or not.

For an example:
I'd declare a variable like this:

 @CleanAfterUse
 private Foo foo;

And that annotation would be responsible for implementing ThreadLocal behind the scenes and setting, removing values after used.