我问了一个常见的Spring问题:自动转换Spring bean,很多人回答说应该尽可能避免调用Spring的ApplicationContext.getBean()。为什么呢?

我还应该如何访问我配置Spring创建的bean呢?

我在一个非web应用程序中使用Spring,并计划访问LiorH所描述的共享ApplicationContext对象。

修正案

我接受下面的答案,但这里有Martin Fowler的另一种观点,他讨论了依赖注入与使用服务定位器(本质上与调用包装的ApplicationContext.getBean()相同)的优点。

In part, Fowler states, "With service locator the application class asks for it [the service] explicitly by a message to the locator. With injection there is no explicit request, the service appears in the application class - hence the inversion of control. Inversion of control is a common feature of frameworks, but it's something that comes at a price. It tends to be hard to understand and leads to problems when you are trying to debug. So on the whole I prefer to avoid it [Inversion of Control] unless I need it. This isn't to say it's a bad thing, just that I think it needs to justify itself over the more straightforward alternative."


当前回答

你应该使用:ConfigurableApplicationContext而不是for ApplicationContext

其他回答

其他人指出了普遍的问题(并且是有效的答案),但我只想提供一个额外的评论:并不是说你永远不应该这样做,而是尽可能少地做。

通常这意味着它只执行一次:在引导期间。然后,它只是访问“根”bean,通过它可以解决其他依赖关系。这可以是可重用的代码,如基本servlet(如果开发web应用程序)。

使用@Autowired或ApplicationContext.getBean()实际上是一回事。通过这两种方式,您可以获得在您的上下文中配置的bean,并且通过这两种方式,您的代码都依赖于spring。 你唯一应该避免的是实例化你的ApplicationContext。只做一次!换句话说,一条线就像

ApplicationContext context = new ClassPathXmlApplicationContext("AppContext.xml");

在应用程序中只应使用一次。

There is another time when using getBean makes sense. If you're reconfiguring a system that already exists, where the dependencies are not explicitly called out in spring context files. You can start the process by putting in calls to getBean, so that you don't have to wire it all up at once. This way you can slowly build up your spring configuration putting each piece in place over time and getting the bits lined up properly. The calls to getBean will eventually be replaced, but as you understand the structure of the code, or lack there of, you can start the process of wiring more and more beans and using fewer and fewer calls to getBean.

但是,仍然有一些情况需要使用服务定位器模式。 例如,我有一个控制器bean,这个控制器可能有一些默认的服务bean,这些服务bean可以通过配置注入依赖项。 虽然这个控制器现在或以后还可以调用许多附加的或新的服务,但这些服务需要服务定位器来检索服务bean。

Spring的前提之一是避免耦合。定义和使用接口,DI, AOP,避免使用ApplicationContext.getBean():-)