解析web.xml中常常需要配置几个Spring核心类

1.org.springframework.web.util.IntrospectorCleanupListener. 在web.xml中&＃xff0c;我们常常的配置如下。

org.springframework.web.util.IntrospectorCleanupListener
它的主要作用是负责处理因JavaBean Inteceptor的使用而引起的缓存泄露问题。Spring 的文档中&＃xff0c;对这个类进行了详细的说明(Spring 3.x)。

* Listener that flushes the JDK&＃39;s {&＃64;link java.beans.Introspector JavaBeans Introspector}* cache on web app shutdown. 在web.xml文件中&＃xff0c;注册这个监听器保证恰到地释放web应用程序类加载及它所加载的

* 类(Register this listener in your web.xml to) guarantee proper release of

* the web application class loader and its loaded classes.

**

If the JavaBeans Introspector has been used to analyze application classes,* the system-level Introspector cache will hold a hard reference to those classes.* Consequently, those classes and the web application class loader will not be* garbage-collected on web app shutdown! This listener performs proper cleanup,* to allow for garbage collection to take effect.**

Unfortunately, the only way to clean up the Introspector is to flush* the entire cache, as there is no way to specifically determine the* application&＃39;s classes referenced there. This will remove cached* introspection results for all other applications in the server too.**

Note that this listener is not necessary when using Spring&＃39;s beans* infrastructure within the application, as Spring&＃39;s own introspection results* cache will immediately flush an analyzed class from the JavaBeans Introspector* cache and only hold a cache within the application&＃39;s own ClassLoader.** Although Spring itself does not create JDK Introspector leaks, note that this* listener should nevertheless be used in scenarios where the Spring framework classes* themselves reside in a &＃39;common&＃39; ClassLoader (such as the system ClassLoader).* In such a scenario, this listener will properly clean up Spring&＃39;s introspection cache.**

Application classes hardly ever need to use the JavaBeans Introspector* directly, so are normally not the cause of Introspector resource leaks.* Rather, many libraries and frameworks do not clean up the Introspector:* e.g. Struts and Quartz.(当然啦&＃xff0c;许多库包和框架不会清理拦截器&＃xff0c;如Struts 和 Quartz)* 既然这样&＃xff0c;这样一个简单的缓存泄露会引起整个web引用程序的类加载不能被垃圾回收器回收。

*

Note that a single such Introspector leak will cause the entire web* app class loader to not get garbage collected! This has the consequence that* you will see all the application&＃39;s static class resources (like singletons)* around after web app shutdown, which is not the fault of those classes!**

This listener should be registered as the first one in web.xml,* before any application listeners such as Spring&＃39;s ContextLoaderListener.* This allows the listener to take full effect at the right time of the lifecycle.

正如文档中所说的&＃xff0c;“在web.xml中&＃xff0c;这个监听器应该在任何应用程序监听器&＃xff0c;比如Spring&＃39;s ContextLoaderListener之前,作为第一个监听器被注册(上面文档最后一段)。在应用程序运行周期的正确时刻&＃xff0c;让监听器充分发挥作用” 。

2.org.springframework.web.context.ContextLoaderListener. 这个类是程序引导监听器去开启和关闭Spring的Root&＃xff0c;它注册在web.xml文件中的org.springframework.web.util.Log4jConfigListener配置之后。

3.org.springframework.web.context.request.RequestContextListener. 它显露Request给当前的线程(Current Thread). 这个类主要用作第三方servlet&＃xff0c;例如the JSF FacesServlet。在Spring自己的web支持下&＃xff0c; DispatcherServlet的处理是相当地有能力的