概述
Spring针对Java Transaction API (JTA)、JDBC、Hibernate和Java Persistence API(JPA)等事务 API，实现了一致的编程模型，而Spring的声明式事务功能更是提供了极其方便的事务配置方式，配合Spring Boot的自动配置，大多数Spring Boot项目只需要在方法上标记@Transactional注解，即可一键开启方法的事务性配置。
但是，事务如果没有被正确出，很有可能会导致事务的失效，带来意想不到的数据不一致问题，随后就是大量的人工接入查看和修复数据，该篇主要分享Spring事务在技术上的正确使用方式，避免因为事务处理不当导致业务逻辑产生大量偶发性BUG。
在分析事务失效的常见场景之前，我们先来了解一下：事务的传播类型 和 @Transactionnal 注解的不同属性的含义。
事务的传播类型
//如果有事务, 那么加入事务, 没有的话新建一个(默认)
@Transactional(propagation=Propagation.REQUIRED)
//容器不为这个方法开启事务
@Transactional(propagation=Propagation.NOT_SUPPORTED)
//不管是否存在事务, 都创建一个新的事务, 原来的挂起, 新的执行完毕, 继续执行老的事务
@Transactional(propagation=Propagation.REQUIRES_NEW)
//必须在一个已有的事务中执行, 否则抛出异常
@Transactional(propagation=Propagation.MANDATORY)
//必须在一个没有的事务中执行, 否则抛出异常(与Propagation.MANDATORY相反)
@Transactional(propagation=Propagation.NEVER)
//如果其他bean调用这个方法, 在其他bean中声明事务, 那就用事务, 如果其他bean没有声明事务, 那就不用事务
@Transactional(propagation=Propagation.SUPPORTS)
isolation
该属性用于设置底层数据库的事务隔离级别，事务的隔离级别介绍：
// 读取未提交数据(会出现脏读, 不可重复读) 基本不使用
@Transactional(isolation = Isolation.READ_UNCOMMITTED)
// 读取已提交数据(会出现不可重复读和幻读) Oracle默认
@Transactional(isolation = Isolation.READ_COMMITTED)
// 可重复读(会出现幻读) MySQL默认
@Transactional(isolation = Isolation.REPEATABLE_READ)
// 串行化
@Transactional(isolation = Isolation.SERIALIZABLE)
@Transactionnal注解属性
@Transactional注解可以作用于接口、接口方法、类以及类方法上，它可以通过不同的参数来选择什么类型Exception异常下执行回滚或者不回滚操作。
Spring事务失效的场景
1. 事务方法未被Spring管理
如果事务方法所在的类没有注册到Spring IOC容器中，也就是说，事务方法所在类并没有被Spring管理，则Spring事务会失效，举个例子🌰：
/**
* 商品业务实现层
*
* @author: austin
* @since: 2023/2/10 14:19
*/
public class ProductServiceImpl extends ServiceImpl<ProductMapper, Product> implements IProductService {
@Autowired
private ProductMapper productMapper;
@Override
@Transactional(propagation = Propagation.REQUIRES_NEW)
public void updateProductStockById(Integer stockCount, Long productId) {
productMapper.updateProductStockById(stockCount, productId);
}
}
ProductServiceImpl实现类上没有添加@Service注解，Product的实例也就没有被加载到Spring IOC容器，此时updateProductStockById()方法的事务就会在Spring中失效。
2. 方法使用final类型修饰
有时候，某个方法不想被子类重新，这时可以将该方法定义成final的。普通方法这样定义是没问题的，但如果将事务方法定义成final，例如：
@Service
public class OrderServiceImpl {
@Transactional
public final void cancel(OrderDTO orderDTO) {
// 取消订单
cancelOrder(orderDTO);
}
}
OrderServiceImpl的cancel取消订单方法被final修饰符修饰，Spring事务底层使用了AOP，也就是通过JDK动态代理或者cglib，帮我们生成了代理类，在代理类中实现的事务功能。但如果某个方法用final修饰了，那么在它的代理类中，就无法重写该方法，从而无法添加事务功能。这种情况事务就会在Spring中失效。
💡Tips: 如果某个方法是static的，同样无法通过动态代理将方法声明为事务方法。
3. 非public修饰的方法
如果事务方式不是public修饰，此时Spring事务会失效，举个例子🌰：
/**
* 商品业务实现层
*
* @author: austin
* @since: 2023/2/10 14:19
*/
@Service
public class ProductServiceImpl extends ServiceImpl<ProductMapper, Product> implements IProductService {
@Autowired
private ProductMapper productMapper;
@Override
@Transactional(propagation = Propagation.REQUIRES_NEW)
private void updateProductStockById(Integer stockCount, String productId) {
productMapper.updateProductStockById(stockCount, productId);
}
}
虽然ProductServiceImpl添加了@Service注解，同时updateProductStockById()方法上添加了@Transactional(propagation = Propagation.REQUIRES_NEW)注解，但是由于事务方法updateProductStockById()被 private 定义为方法内私有，同样Spring事务会失效。
4. 同一个类中的方法相互调用
@Service
public class OrderServiceImpl extends ServiceImpl<OrderMapper, Order> implements IOrderService {
@Autowired
private OrderMapper orderMapper;
@Autowired
private ProductMapper productMapper;
@Override
public ResponseEntity submitOrder(Order order) {
// 保存生成订单信息
long orderNo = Math.abs(ThreadLocalRandom.current().nextLong(1000));
order.setOrderNo("ORDER_" + orderNo);
orderMapper.insert(order);
// 扣减库存
this.updateProductStockById(order.getProductId(), 1L);
return new ResponseEntity(HttpStatus.OK);
}
@Transactional(propagation = Propagation.REQUIRES_NEW)
public void updateProductStockById(Integer num, Long productId) {
productMapper.updateProductStockById(num, productId);
}
}
submitOrder()方法和updateProductStockById()方法都在OrderService类中，然而submitOrder()方法没有添加事务注解，updateProductStockById()方法虽然添加了事务注解，这种情况updateProductStockById()会在Spring事务中失效。
5. 方法的事务传播类型不支持事务
如果内部方法的事务传播类型为不支持事务的传播类型，则内部方法的事务同样会在Spring中失效，举个例子：
@Service
public class OrderServiceImpl extends ServiceImpl<OrderMapper, Order> implements IOrderService {
@Autowired
private OrderMapper orderMapper;
@Autowired
private ProductMapper productMapper;
@Override
@Transactional(propagation = Propagation.REQUIRES_NEW)
public ResponseEntity submitOrder(Order order) {
long orderNo = Math.abs(ThreadLocalRandom.current().nextLong(1000));
order.setOrderNo("ORDER_" + orderNo);
orderMapper.insert(order);
// 扣减库存
this.updateProductStockById(order.getProductId(), 1L);
return new ResponseEntity(HttpStatus.OK);
}
/**
* 扣减库存方法事务类型声明为NOT_SUPPORTED不支持事务的传播
*/
@Transactional(propagation = Propagation.NOT_SUPPORTED)
public void updateProductStockById(Integer num, Long productId) {
productMapper.updateProductStockById(num, productId);
}
}
6. 异常被内部catch，程序生吞异常
@Service
public class OrderServiceImpl extends ServiceImpl<OrderMapper, Order> implements IOrderService {
@Autowired
private OrderMapper orderMapper;
@Autowired
private ProductMapper productMapper;
@Override
@Transactional(propagation = Propagation.REQUIRES_NEW)
public ResponseEntity submitOrder(Order order) {
long orderNo = Math.abs(ThreadLocalRandom.current().nextLong(1000));
order.setOrderNo("ORDER_" + orderNo);
orderMapper.insert(order);
// 扣减库存
this.updateProductStockById(order.getProductId(), 1L);
return new ResponseEntity(HttpStatus.OK);
}
/**
* 扣减库存方法事务类型声明为NOT_SUPPORTED不支持事务的传播
*/
@Transactional(propagation = Propagation.NOT_SUPPORTED)
public void updateProductStockById(Integer num, Long productId) {
try {
productMapper.updateProductStockById(num, productId);
} catch (Exception e) {
// 这里仅仅是捕获异常之后的打印（相当于程序吞掉了异常）
log.error("Error updating product Stock: {}", e);
}
}
}
7. 数据库不支持事务
Spring事务生效的前提是连接的数据库支持事务，如果底层的数据库都不支持事务，则Spring事务肯定会失效的，例如🌰：使用MySQL数据库，选用MyISAM存储引擎，因为MyISAM存储引擎本身不支持事务，因此事务毫无疑问会失效。
8. 未配置开启事务
如果项目中没有配置Spring的事务管理器，即使使用了Spring的事务管理功能，Spring的事务也不会生效，例如，如果你是Spring Boot项目，没有在SpringBoot项目中配置如下代码：
@Bean
public PlatformTransactionManager transactionManager(DataSource dataSource) {
return new DataSourceTransactionManager(dataSource);
}
如果是以往的Spring MVC项目，如果没有配置下面的代码，Spring事务也不会生效，正常需要在applicationContext.xml文件中，手动配置事务相关参数，比如：
<!-- 配置事务管理器 -->
<bean class="org.springframework.jdbc.datasource.DataSourceTransactionManager" id="transactionManager">
<property name="dataSource" ref="dataSource"></property>
</bean>
<tx:advice id="advice" transaction-manager="transactionManager">
<tx:attributes>
<tx:method name="*" propagation="REQUIRED"/>
</tx:attributes>
</tx:advice>
<!-- 用切点把事务切进去 -->
<aop:config>
<aop:pointcut expression="execution(* com.universal.ubdk.*.*(..))" id="pointcut"/>
<aop:advisor advice-ref="advice" pointcut-ref="pointcut"/>
</aop:config>
9. 错误的传播特性
其实，我们在使用@Transactional注解时，是可以指定propagation参数的。
该参数的作用是指定事务的传播特性，目前Spring支持7种传播特性：
-
REQUIRED如果当前上下文中存在事务，那么加入该事务，如果不存在事务，创建一个事务，这是默认的传播属性值。 -
SUPPORTS如果当前上下文存在事务，则支持事务加入事务，如果不存在事务，则使用非事务的方式执行。 -
MANDATORY如果当前上下文中存在事务，否则抛出异常。 -
REQUIRES_NEW每次都会新建一个事务，并且同时将上下文中的事务挂起，执行当前新建事务完成以后，上下文事务恢复再执行。 -
NOT_SUPPORTED如果当前上下文中存在事务，则挂起当前事务，然后新的方法在没有事务的环境中执行。 -
NEVER如果当前上下文中存在事务，则抛出异常，否则在无事务环境上执行代码。 -
NESTED如果当前上下文中存在事务，则嵌套事务执行，如果不存在事务，则新建事务。
如果我们在手动设置propagation参数的时候，把传播特性设置错了，比如：
@Service
public class OrderServiceImpl {
@Transactional(propagation = Propagation.NEVER)
public void cancelOrder(UserModel userModel) {
// 取消订单
cancelOrder(orderDTO);
// 还原库存
restoreProductStock(orderDTO.getProductId(), orderDTO.getProductCount());
}
}
我们可以看到cancelOrder()方法的事务传播特性定义成了Propagation.NEVER，这种类型的传播特性不支持事务，如果有事务则会抛异常。
10. 多线程调用
在实际项目开发中，多线程的使用场景还是挺多的。如果Spring事务用在多线程场景中使用不当，也会导致事务无法生效。
@Slf4j
@Service
public class OrderServiceImpl {
@Autowired
private OrderMapper orderMapper;
@Autowired
private MessageService messageService;
@Transactional
public void orderCommit(orderModel orderModel) throws Exception {
orderMapper.insertOrder(orderModel);
new Thread(() -> {
messageService.sendSms();
}).start();
}
}
@Service
public class MessageService {
@Transactional
public void sendSms() {
// 发送短信
}
}
通过示例，我们可以看到订单提交的事务方法orderCommit()中，调用了发送短信的事务方法sendSms()，但是发送短信的事务方法sendSms()是另起了一个线程调用的。
这样会导致两个方法不在同一个线程中，从而是两个不同的事务。如果是sendSms()方法中抛了异常，orderCommit()方法也回滚是不可能的。
实际上，Spring的事务是通过ThreadLocal来保证线程安全的，事务和当前线程绑定，多个线程自然会让事务失效。
总结
本篇文章主要是介绍Spring事务传播特性，阐明了@Transactional注解属性的使用方式，通过不同的代码示例演示了Spring事务失效的常见场景，如果文章对你有所帮助，欢迎 点赞👍+评论💬+收藏❤
作者：austin流川枫
来源：juejin.cn/post/7198894062534475834
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原文始发于微信公众号（Java知音）：我认真总结并分析了 Spring 事务失效的十种常见场景
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