Action类可以限定为Singleton吗？ [英] Can an Action class be scoped to Singleton?

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.

推荐答案

1. 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。

1. 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

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