Spring 事务失效的八种场景

1. 抛出检查异常导致事务不能正确回滚

@Service
public class Service1 {

    @Autowired
    private AccountMapper accountMapper;

    @Transactional
    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);
        }
    }
}

• 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 {

    @Autowired
    private 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 {

    @Autowired
    private 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 {

    @Autowired
    private AccountMapper accountMapper;

    @Transactional
    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);
        }
    }
}

• 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 {

    @Autowired
    private 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 {

    @Autowired
    public 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 {

	@Autowired
	private 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);

    @Autowired
    private 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);

    @Autowired
    private 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