使用jpa注释在一个事务中保存数据，并在另一个事务中提取数据

@Entity
@Table(name = "user")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;

    // 其他字段和关联关系的定义...

    // 省略getter和setter方法...
}

public interface UserRepository extends JpaRepository<User, Long> {
    // 自定义查询方法...
}

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

    public void saveUser(User user) {
        userRepository.save(user);
    }

    public User getUserById(Long id) {
        return userRepository.findById(id).orElse(null);
    }
}

@RestController
@RequestMapping("/users")
public class UserController {
    @Autowired
    private UserService userService;

    @PostMapping
    public void saveUser(@RequestBody User user) {
        userService.saveUser(user);
    }

    @GetMapping("/{id}")
    public User getUserById(@PathVariable Long id) {
        return userService.getUserById(id);
    }
}