@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;

    @Cacheable(value = "users", key = "#userId")
    public User getUserById(Long userId) {
        return userRepository.findById(userId).orElse(null);
    }

    @CachePut(value = "users", key = "#user.id")
    // @CachePut(value = "users", key = "#user.id + '_' + #user.age")
    public User updateUser(User user) {
        userRepository.save(user);
        return user;
    }

    @CacheEvict(value = "users", key = "#userId")
    public void deleteUser(Long userId) {
        userRepository.deleteById(userId);
    }

    @CacheEvict(value = "users", allEntries = true)
    public void clearCache() {
        // 清空缓存
    }
}