JEE7：EJB和CDI bean是否支持容器管理的事务？ [英] JEE7: Do EJB and CDI beans support container-managed transactions?

问题描述

Java EE7由一堆bean定义组成：

• Managed Bean 1.0（JSR-316 / JSR-250）


• Java 1.0的依赖注入（JSR-330）


• CDI 1.1（JSR-346）


• JSF管理Bean 2.2（JSR-344）


• EJB 3.2（JSR-345）

为了摆脱我心中的混乱，我研究了几篇文章何时使用哪种豆类。 EJB 的优点之一似乎是，它们独自支持声明性容器管理的事务（着名的事务注释）。我不知道，如果这是正确的。有人可以批准吗？

同时，我想出了一个简单的演示应用程序来检查这是否真的是真的。我刚刚定义了一个CDI bean（ 不是 一个EJB - 它没有类级别的注释）如下，基于此片段：

  public class CdiBean {
 @Resource 
 TransactionSynchronizationRegistry tsr; 
 
 @Transactional（Transactional.TxType.REQUIRED）
 public boolean isTransactional（）{
 return tsr.getTransactionStatus（）== Status.STATUS_ACTIVE; 
} 
} 
  

现在，GlassFish 4.0的结果是这种方法实际上返回true，根据我的查询， 不按预期工作 。我确实期望容器忽略CDI bean方法上的@Transactional注释，甚至抛出异常。我使用新安装的GlassFish 4服务器，所以没有干扰。

所以我的问题是真的：

• 哪些bean类型实际上支持容器管理的事务？


• 只是为了好奇，我如何使用一个简单的演示应用程序来测试它，上面的代码是错误的？

（BTW：有人描述了类似的问题这里，但其解决方案不适用于我的情况。

解决方案

由于Java EE 7只有EJB是事务性的，而 @Transactional 注释不存在。 Java EE 7和JTA 1.2可以在CDI中使用事务拦截器，使用 @Transactional 注释。

回答您的问题关于最好的bean类型，默认情况下是CDI。

CDI bean更轻并且支持许多功能（包括作为EJB），并且默认情况下激活（当您将 beans.xml 文件添加到您的应用程序时）。
由于Java EE 6 @Inject supersede @EJB 。即使您使用远程EJB（CDI中不存在功能），最佳做法表明您一次注入远程EJB和CDI生产者将其显示为CDI bean

  public class Resources {
 
 @EJB 
 @Produces 
 MyRemoteEJB ejb ; 
 
} 
  

同样的建议用于Java EE资源

  public class Resources2 {
 
 @PersistenceContext 
 @Produces 
 EntityManager em; 
 
} 
  

这些生产者将在稍后使用

  public class MyBean {
 
 @Inject 
 MyRemoteEJB bean; 
 
 @Inject 
 EntityManager em; 
 
} 
  

EJB对于JMS中包含的某些服务继续有意义或异步处理，但您将使用它们作为CDI bean。

Java EE7 consists of a bunch of "bean" definitions:

• Managed Beans 1.0 (JSR-316 / JSR-250)
• Dependency Injection for Java 1.0 (JSR-330)
• CDI 1.1 (JSR-346)
• JSF Managed Beans 2.2 (JSR-344)
• EJB 3.2 (JSR-345)

In order to get rid of the chaos in my mind, I studies several articles of "when to use which bean type". One of the pros for EJB seems to be that they alone support declarative container-managed transactions (the famous transaction annotations). I'm not sure, though, if this is correct. Can anyone approve this?

Meanwhile, I came up with a simple demo application to check if this was actually true. I just defined a CDI bean (not an EJB - it has no class level annotations) as follows, based on this snippet:

public class CdiBean {
    @Resource
    TransactionSynchronizationRegistry tsr;

    @Transactional(Transactional.TxType.REQUIRED)
    public boolean isTransactional() {
        return tsr.getTransactionStatus() == Status.STATUS_ACTIVE;
    }
}

Now, the outcome on GlassFish 4.0 is that this method actually returns true, which, according to my inquiries, is not working as expected. I did expect the container to ignore the @Transactional annotation on a CDI bean method, or to even throw an exception. I use a freshly-installed GlassFish 4 server, so there are no interferences.

So my question is really:

• Which bean types do actually support container-managed transactions?
• Just for the sake of curiosity, how could I test it with a simple demo application if the code above is wrong?

(BTW: Someone described a similar problem here, but its solution does not apply to my case.

解决方案

Until Java EE 7 only EJB was transactional and the @Transactional annotation didn't exist.

Since Java EE 7 and JTA 1.2 you can use transactional interceptor in CDI with @Transactional annotation.

To answer your question about the best type of bean to use, the answer is CDI by default.

CDI beans are lighter than EJB and support a lot of feature (including being an EJB) and is activated by default (when you add beans.xml file to your app). Since Java EE 6 @Inject supersede @EJB. Even if you use remote EJBs (feature not existing in CDI) the best practice suggest that you @EJB once to inject remote EJB and a CDI producer to expose it as a CDI bean

public class Resources {

    @EJB
    @Produces
    MyRemoteEJB ejb;

}

The same is suggested for Java EE resources

public class Resources2 {

    @PersistenceContext
    @Produces
    EntityManager em;

}

These producers will be used later

public class MyBean {

    @Inject
    MyRemoteEJB bean;

    @Inject
    EntityManager em;

}

EJB continue to make sense for certain services they include like JMS or Asynchronous treatment, but you'll use them as CDI bean.

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