it is said that springmvc is thread-safe. I know that stateless objects must be thread-safe. But when Service is injected into Controller, it becomes a stateful object . Is it still thread-safe?

//
public class UserController {
    
}

//
public class UserController {

    int a;
    
}

//?????
public class UserController {

    @AutoWired
    private UserService userService;
    
}

I hope the person who knows it will solve the problem for my younger brother. Thank you!
add: I know about ThreadLocal and single-case multiple cases (scope=prototype). I just want to know the stateless and stateless situations I described above.