1. 抛出检查异常导致事务不能正确回滚
@Service
public class Service1 {@Autowiredprivate AccountMapper accountMapper;@Transactionalpublic void transfer(int from, int to, int amount) throws FileNotFoundException {int fromBalance = accountMapper.findBalanceBy(from);if (fromBalance - amount >= 0) {accountMapper.update(from, -1 * amount);new FileInputStream("aaa");accountMapper.update(to, amount);}}
}
- 原因:Spring 默认只会回滚非检查异常
- 解法:配置 rollbackFor 属性
@Transactional(rollbackFor = Exception.class)
2. 业务方法内自己 try-catch 异常导致事务不能正确回滚
@Service
public class Service2 {@Autowiredprivate AccountMapper accountMapper;@Transactional(rollbackFor = Exception.class)public void transfer(int from, int to, int amount) {try {int fromBalance = accountMapper.findBalanceBy(from);if (fromBalance - amount >= 0) {accountMapper.update(from, -1 * amount);new FileInputStream("aaa");accountMapper.update(to, amount);}} catch (FileNotFoundException e) {e.printStackTrace();}}
}
- 原因:事务通知只有捉到了目标抛出的异常,才能进行后续的回滚处理,如果目标自己处理掉异常,事务通知无法知悉
- 解法1:异常原样抛出:
在 catch 块添加
throw new RuntimeException(e);
解法2:手动设置 TransactionStatus.setRollbackOnly()
在 catch 块添加
TransactionInterceptor.currentTransactionStatus().setRollbackOnly();
3. aop 切面顺序导致导致事务不能正确回滚
@Service
public class Service3 {@Autowiredprivate AccountMapper accountMapper;@Transactional(rollbackFor = Exception.class)public void transfer(int from, int to, int amount) throws FileNotFoundException {int fromBalance = accountMapper.findBalanceBy(from);if (fromBalance - amount >= 0) {accountMapper.update(from, -1 * amount);new FileInputStream("aaa");accountMapper.update(to, amount);}}
}
@Aspect
public class MyAspect {@Around("execution(* transfer(..))")public Object around(ProceedingJoinPoint pjp) throws Throwable {LoggerUtils.get().debug("log:{}", pjp.getTarget());try {return pjp.proceed();} catch (Throwable e) {e.printStackTrace();return null;}}
}
-
原因:事务切面优先级最低,但如果自定义的切面优先级和他一样,则还是自定义切面在内层,这时若自定义切面没有正确抛出异常…
-
解法1、2:同情况2 中的解法:1、2
-
解法3:调整切面顺序,在 MyAspect 上添加
@Order(Ordered.LOWEST_PRECEDENCE - 1)
(不推荐)
4. 非 public 方法导致的事务失效
@Service
public class Service4 {@Autowiredprivate AccountMapper accountMapper;@Transactionalvoid transfer(int from, int to, int amount) throws FileNotFoundException {int fromBalance = accountMapper.findBalanceBy(from);if (fromBalance - amount >= 0) {accountMapper.update(from, -1 * amount);accountMapper.update(to, amount);}}
}
-
原因:Spring 为方法创建代理、添加事务通知、前提条件都是该方法是 public 的
-
解法1:改为 public 方法
-
解法2:添加 bean 配置如下(不推荐)
@Bean
public TransactionAttributeSource transactionAttributeSource() {return new AnnotationTransactionAttributeSource(false);
}
5. 父子容器导致的事务失效
@Service
public class Service5 {@Autowiredprivate AccountMapper accountMapper;@Transactional(rollbackFor = Exception.class)public void transfer(int from, int to, int amount) throws FileNotFoundException {int fromBalance = accountMapper.findBalanceBy(from);if (fromBalance - amount >= 0) {accountMapper.update(from, -1 * amount);accountMapper.update(to, amount);}}
}
控制器类:
@Controller
public class AccountController {@Autowiredpublic Service5 service;public void transfer(int from, int to, int amount) throws FileNotFoundException {service.transfer(from, to, amount);}
}
App 配置类
@Configuration
@ComponentScan("day04.tx.app.service")
@EnableTransactionManagement
// ...
public class AppConfig {// ... 有事务相关配置
}
Web 配置类
@Configuration
@ComponentScan("day04.tx.app")
// ...
public class WebConfig {// ... 无事务配置
}
现在配置了父子容器,WebConfig 对应子容器,AppConfig 对应父容器,发现事务依然失效
-
原因:子容器扫描范围过大,把未加事务配置的 service 扫描进来
-
解法1:各扫描各的,不要图简便
-
解法2:不要用父子容器,所有 bean 放在同一容器
6. 调用本类方法导致传播行为失效
@Service
public class Service6 {@Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class)public void foo() throws FileNotFoundException {LoggerUtils.get().debug("foo");bar();}@Transactional(propagation = Propagation.REQUIRES_NEW, rollbackFor = Exception.class)public void bar() throws FileNotFoundException {LoggerUtils.get().debug("bar");}
}
- 原因:本类方法调用不经过代理,因此无法增强
- 解法1:依赖注入自己(代理)来调用
- 解法2:通过 AopContext 拿到代理对象,来调用
- 解法3:通过 CTW,LTW 实现功能增强
解法1:
@Service
public class Service6 {@Autowiredprivate Service6 proxy; // 本质上是一种循环依赖@Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class)public void foo() throws FileNotFoundException {LoggerUtils.get().debug("foo");System.out.println(proxy.getClass());proxy.bar();}@Transactional(propagation = Propagation.REQUIRES_NEW, rollbackFor = Exception.class)public void bar() throws FileNotFoundException {LoggerUtils.get().debug("bar");}
}
解法2:还需要在 AppConfig 上添加 @EnableAspectJAutoProxy(exposeProxy = true)
@Service
public class Service6 {@Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class)public void foo() throws FileNotFoundException {LoggerUtils.get().debug("foo");((Service6) AopContext.currentProxy()).bar();}@Transactional(propagation = Propagation.REQUIRES_NEW, rollbackFor = Exception.class)public void bar() throws FileNotFoundException {LoggerUtils.get().debug("bar");}
}
7. @Transactional 没有保证原子行为
@Service
public class Service7 {private static final Logger logger = LoggerFactory.getLogger(Service7.class);@Autowiredprivate AccountMapper accountMapper;@Transactional(rollbackFor = Exception.class)public void transfer(int from, int to, int amount) {int fromBalance = accountMapper.findBalanceBy(from);logger.debug("更新前查询余额为: {}", fromBalance);if (fromBalance - amount >= 0) {accountMapper.update(from, -1 * amount);accountMapper.update(to, amount);}}public int findBalance(int accountNo) {return accountMapper.findBalanceBy(accountNo);}
}
上面的代码实际上是有 bug 的,假设 from 余额为 1000,两个线程都来转账 1000,可能会出现扣减为负数的情况
- 原因:事务的原子性仅涵盖 insert、update、delete、select … for update 语句,select 方法并不阻塞
如上图所示,红色线程和蓝色线程的查询都发生在扣减之前,都以为自己有足够的余额做扣减
8. @Transactional 方法导致的 synchronized 失效
针对上面的问题,能否在方法上加 synchronized 锁来解决呢?
@Service
public class Service7 {private static final Logger logger = LoggerFactory.getLogger(Service7.class);@Autowiredprivate AccountMapper accountMapper;@Transactional(rollbackFor = Exception.class)public synchronized void transfer(int from, int to, int amount) {int fromBalance = accountMapper.findBalanceBy(from);logger.debug("更新前查询余额为: {}", fromBalance);if (fromBalance - amount >= 0) {accountMapper.update(from, -1 * amount);accountMapper.update(to, amount);}}public int findBalance(int accountNo) {return accountMapper.findBalanceBy(accountNo);}
}
答案是不行,原因如下:
-
synchronized 保证的仅是目标方法的原子性,环绕目标方法的还有 commit 等操作,它们并未处于 sync 块内
-
可以参考下图发现,蓝色线程的查询只要在红色线程提交之前执行,那么依然会查询到有 1000 足够余额来转账
-
解法1:synchronized 范围应扩大至代理方法调用
-
解法2:使用 select … for update 替换 select