Action类可以限定为Singleton吗？

问题描述：

我的问题不仅仅是动作类可以限定为单例，而且我还想知道哪些是最佳实践。两者都在Struts2和Spring的背景下。控制器和模型的最佳VIEW范围（比如请求或会话）。

My question is not only if action classes can be scoped to singleton, but I also want to know which are the best practices. Both in context of Struts2 and Spring. Best scope of VIEW (say request or session), for controller and model.

答

Struts2操作由Struts容器管理。它们是ThreadLocal，因此每个请求都有自己的Action的线程安全副本。

Struts2 Actions are managed by the Struts Container. They are ThreadLocal, hence every request has its own thread-safe copy of the Action.

如果你使用Spring通过 Struts2-Spring-plugin ，有多种使用级别：

If you use Spring to handle them through the Struts2-Spring-plugin, there are multiple levels of usage:

你可以让Struts容器实例化它们，并通过Spring处理它们以进行依赖注入，或者

你可以让Spring接管它们控制并对每个行动的整个生命周期负全部责任。
在第二种情况下：
- 如果在Spring XML配置文件中将操作声明为bean，则操作将获得默认的Spring范围，这是Singleton（ scope =singleton）。这是危险的，无用的，99.99％的时间不是你想要的，因为你将失去框架能力的基本部分，行动将变成种类的servlet，线程 - UNsafe，并且会出现许多问题;
- 为了防止这种情况，你可以在bean声明中放入 scope =prototype，这样就可以让Spring实例化影响其性质。
- you can let the Struts container instantiate them, and handle them through Spring for the Dependency Injection, or
- you can let Spring take over control and be fully responsible for the whole lifecycle of every Action.
  In this second case:
  - if you declare an action as a bean in a Spring XML configuration file, the action will get the default Spring scope, that is Singleton (scope="singleton"). THIS IS DANGEROUS, USELESS, and 99.99% of the times NOT WHAT YOU WANT, because you will lose a fundamental part of the framework capability, actions will be turned into kind-of servlets, thread-UNsafe, and many problems will arise;
  - to prevent that, you can put the scope="prototype" in the bean declaration, that will let Spring instantiate the action without affecting its nature.
  如果你在容器Java EE中6+兼容（例如，Jboss 7，Wildfly 8，TomEE 1.7，Glassfish 3 +，ecc ...），上下文和依赖注入通过CDI处理。如果需要，您可以使用 Struts2-CDI-plugin 来允许CDI通过 @处理您的操作并注入依赖项注入 注释（而不是 @Autowired 一个）
  
  If you are inside a container Java EE 6+ compliant (for example, Jboss 7, Wildfly 8, TomEE 1.7, Glassfish 3+, ecc...), the Contexts and the Dependency Injections are handled through CDI. If you want, you can use the Struts2-CDI-plugin to allow CDI to handle your actions and inject dependencies through the @Inject annotation (instead of the @Autowired one)
  
  我过去经常使用Spring，然后在发现CDI和CDI插件后，我已经切换并且从未回头，所以我投票给n.3
  
  I've used Spring a lot in the past, then after discovering CDI and the CDI plugin, I've switched and never looked back, so I vote for the n.3

Action类可以限定为Singleton吗？

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