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3. 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();
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
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
- 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
