Spring 事务失效

要求

  • 掌握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();
....
} catch (FileNotFoundException e) {
            e.printStackTrace();
            //解法1:异常原样抛出
            // throw new RuntimeException(e);
            // 解法2:手动设置 TransactionStatus.setRollbackOnly()
            // 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

spring boot 就一个容器, spring + spring mvc 有父子容器

package day04.tx.app.service;

// ...

@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

package day04.tx.app.controller;

// ...

@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
    Spring 事务失效_第1张图片

  • 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
    Spring 事务失效_第2张图片
  • 解法1:synchronized 范围应扩大至代理方法调用
        Service7 bean = context.getBean(Service7.class);
        Object lock = new Object();

        CountDownLatch latch = new CountDownLatch(2);
        new MyThread(() -> {
           synchronized (lock) {
                bean.transfer(1, 2, 1000);
            }
            latch.countDown();
        }, "t1", "boldMagenta").start();

        new MyThread(() -> {
           synchronized (lock) {
                bean.transfer(1, 2, 1000);
            }
            latch.countDown();
        }, "t2", "boldBlue").start();

        latch.await();
        System.out.println(bean.findBalance(1));
    }
  • 解法2:使用 select … for update 替换 select

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