ConstraintViolationException最后不也抛出了，为什么没被catch到？
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ConstraintViolationException最后不也抛出了，为什么没被catch到？
上周，我们通过这篇文章《为什么catch了异常，但事务还是回滚了？》来解释了，之前test4为什么会回滚的原因。
但还是收到了很多没有理解的反馈，主要是根据前文给出的线索去跟踪，是获得到了回滚的标示和异常，而让大家不理解的是，javax.validation.ConstraintViolationException异常不是最后也向外抛出了，那么为什么test4里catch没有能够捕获到呢？
其实这个问题并不难解释，下面就通过这篇文章，做个小实验，帮助大家进一步理解大家的这个疑问！
如果你还不了解这篇文章在讨论什么，建议先看之前的两篇：
动手尝试一下
由于@Transactional注解的事务是通过切面来实现的，所以要通过源码去了解整个过程，可能还是不容易理解。
所以，这里教大家一个简单方法来理解这次test4的catch为什么没有捕获异常。
我们通过类似下面的方式，给test4多加一些日志信息和断点：
同时，记得也在上一篇说到的事务提交入口，也加上断点。
org.springframework.orm.jpa.JpaTransactionManager
然后尝试触发test4的执行，通过DEBUG，我们都可以观察到：
test4中我们加的断点，除了47行没进入，其他的一次性都执行完了。然后才进入了org.springframework.orm.jpa.JpaTransactionManager的doCommit方法。
所以，前文中我们跟踪的事务回滚所抛出的异常，其实是在test4中的try-catch块执行完之后才抛出的，所以内部的这个catch是无法捕获异常的，这里完全就是catch了个寂寞。
通过日志，我们也能观察到这样的执行顺序：
好了，通过这样来看，是不是要比之前有进一步的理解了呢？如果您还想跟深入的了解事务的底层运行机制，一定要debug一下源码，自己过一遍，理解会深刻哦！如果你还有其他疑问，欢迎加入我们的Spring技术交流群，参与交流与讨论，一起学习与进步！如果您正在学习Spring Boot，我的免费教程一直在持续连载，欢迎关注Spring Boot 2.x基础教程。
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