如何判断Java EE 6拦截器中的事务是否处于活动状态？ [英] How to tell if a transaction is active in a Java EE 6 interceptor?

问题描述

我打算为EJB编写拦截器，它基本上会执行以下操作：

I am planning to write an interceptor for an EJB that will do basically the following:

@AroundInvoke
public Object setContext(InvocationContext ctx) throws Exception {
    em.createQuery("... set something [database specific] ...").getSingleResult();
    try {
        return ctx.proceed();
    } finally {
        em.flush();
        em.createQuery("... unset something [database specific] ...").getSingleResult();
    }
}

问题是em.flush（）会抛出一个异常，如果它应用于使用@TransactionAttribute（NOT_SUPPORTED）或@TransactionAttribute（SUPPORTS）注释的方法（即只读方法），而它适用于使用默认@TransactionAttribute（REQUIRED）的方法（即更改数据库的方法） ）。

The problem is that em.flush() throws an exception if it is applied to a method annotated with @TransactionAttribute(NOT_SUPPORTED) or @TransactionAttribute(SUPPORTS) (i.e. read-only methods), while it works fine with methods using the default @TransactionAttribute(REQUIRED) (i.e. methods that change the database).

有没有办法判断交易是否有效，以避免在存在时调用em.flush（）没有当前正在运行的事务，或者我必须创建两个拦截器，一个使用em.flush（），一个没有它？

Is there a way to tell whether a transaction is active in order to avoid the call to em.flush() when there is no transaction currently running, or must I create two interceptors, one with em.flush() and one without it?

我不能注入UserTransaction，因为bean使用容器 - 托管交易。 EntityManager的（em）事务方法仅适用于resource_local事务，而不适用于JTA事务。我需要em.flush（）调用以确保 unset 查询是最后运行的东西。

I cannot inject a UserTransaction since the bean uses container-managed transactions. EntityManager's (em) transaction methods only work with resource_local transactions, not with JTA transactions. I need the em.flush() call to be sure that the unset query is the last thing that runs.

作为奖励问题，是吗谁知道我想做什么是某种不好的做法？我知道拦截器在与bean相同的上下文中运行，因此通过数据库会话分享内容是安全的，但我必须非常小心在退出时取消设置所有内容，因为连接是汇集在一起​​的容器。

As bonus question, does anyone knows if what I am trying to do is some kind of bad practice? I know that the interceptor runs in the same context as the bean, so it will be safe to share things via the database session, but I must be really careful to unset everything on exit because connections are pooled in the container.

推荐答案

你可以注入TransactionSynchronizationRegistry 并使用 getTransactionStatus 获取当前上下文中事务的状态，它返回 int ，这是Status 课程，在您的情况下，您正在寻找 STATUS_NO_TRANSACTION

You can inject a TransactionSynchronizationRegistry and use getTransactionStatus to get the status of the transaction in the current context, it returns an int which is a contant in the Status class, in your case you are looking for STATUS_NO_TRANSACTION

注入：

@Resource
TransactionSynchronizationRegistry tsr;

检查交易状态：

if (Status.STATUS_NO_TRANSACTION == tsr.getTransactionStatus()) {
   // no transaction
}

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