如何获取当前登录Spring的id

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-security</artifactId>
</dependency>

@Service
public class UserDetailsServiceImpl implements UserDetailsService {

    @Autowired
    private UserRepository userRepository;

    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        User user = userRepository.findByUsername(username);
        if (user == null) {
            throw new UsernameNotFoundException("User not found");
        }
        return new org.springframework.security.core.userdetails.User(user.getUsername(), user.getPassword(), new ArrayList<>());
    }
}

@Entity
@Table(name = "users")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String username;

    private String password;

    // 省略其他属性和方法
}

@RestController
public class UserController {

    @GetMapping("/currentUserId")
    public Long getCurrentUserId() {
        Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
        if (authentication.getPrincipal() instanceof UserDetails) {
            UserDetails userDetails = (UserDetails) authentication.getPrincipal();
            // 获取当前登录用户的id
            return userRepository.findByUsername(userDetails.getUsername()).getId();
        }
        return null;
    }
}