@Transactional 注解作用

@Transactional注解是Spring框架中用于管理事务的注解。它可以作用于接口、类、类方法，并且可以配置多个属性信息。当放在类上时，表示该类的所有public方法都使用相同的事务属性信息；当放在方法上时，表示该方法使用自己的事务属性信息，会覆盖类的事务配置信息。@Transactional注解的属性包括propagation、isolation、timeout、readOnly、rollbackFor、noRollbackFor等。其中，propagation属性用于指定事务的传播行为，isolation属性用于指定事务的隔离级别，timeout属性用于指定事务的超时时间，readOnly属性用于指定事务是否只读，rollbackFor属性用于指定哪些异常需要回滚事务，noRollbackFor属性用于指定哪些异常不需要回滚事务。

示例代码如下：

@Service
public class UserServiceImpl implements UserService {

    @Autowired
    private UserDao userDao;

    @Override
    @Transactional(propagation = Propagation.REQUIRED, isolation = Isolation.DEFAULT, readOnly = false, timeout = 36000, rollbackFor = Exception.class)
    public void addUser(User user) {
        userDao.addUser(user);
    }

    @Override
    @Transactional(propagation = Propagation.REQUIRED, isolation = Isolation.DEFAULT, readOnly = false, timeout = 36000, rollbackFor = Exception.class)
    public void updateUser(User user) {
        userDao.updateUser(user);
    }

    @Override
    @Transactional(propagation = Propagation.REQUIRED, isolation = Isolation.DEFAULT, readOnly = false, timeout = 36000, rollbackFor = Exception.class)
    public void deleteUser(int userId) {
        userDao.deleteUser(userId);
    }

    @Override
    @Transactional(propagation = Propagation.SUPPORTS, isolation = Isolation.DEFAULT, readOnly = true, timeout = 36000, rollbackFor = Exception.class)
    public User getUserById(int userId) {
        return userDao.getUserById(userId);
    }

    @Override
    @Transactional(propagation = Propagation.SUPPORTS, isolation = Isolation.DEFAULT, readOnly = true, timeout = 36000, rollbackFor = Exception.class)
    public List<User> getAllUsers() {
        return userDao.getAllUsers();
    }
}