org.springframework.web.util.IntrospectorCleanupListener的用途

偏执的太偏执、 2022-04-13 06:37 165阅读 0赞

完整版见https://jadyer.github.io/2013/09/24/spring-introspector-cleanup-listener/

Spring官方API中对其描述如下

/\*\* 
 \* Listener that flushes the JDK's \{@link java.beans.Introspector JavaBeans Introspector\} 
 \* cache on web app shutdown. Register this listener in your <code>web.xml</code> 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'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's beans 
 \* infrastructure within the application, as Spring's own introspection results 
 \* cache will immediately flush an analyzed class from the JavaBeans Introspector 
 \* cache and only hold a cache within the application'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 'common' ClassLoader (such as the system ClassLoader). 
 \* In such a scenario, this listener will properly clean up Spring'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. 
 \* 
 \* 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'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 <code>web.xml</code>, 
 \* before any application listeners such as Spring's ContextLoaderListener. 
 \* This allows the listener to take full effect at the right time of the lifecycle. 
 \* 
 \* @author Juergen Hoeller 
 \* @since 1.1 
 \* @see java.beans.Introspector\#flushCaches() 
 \* @see org.springframework.beans.CachedIntrospectionResults\#acceptClassLoader 
 \* @see org.springframework.beans.CachedIntrospectionResults\#clearClassLoader 
 \*/ 
翻译过来大致就是下面的意思

/\*\* 
 \* org.springframework.web.util.IntrospectorCleanupListener的用途 
 \* @see ------------------------------------------------------------------------------------------------------------------- 
 \* @see 此监听器出用于主要为了解决java.beans.Introspector导致内存泄漏的问题 
 \* @see 此监听器应该配置在web.xml中与Spring相关监听器中的第一个位置(也要在ContextLoaderListener的前面) 
 \* @see ------------------------------------------------------------------------------------------------------------------- 
 \* @see JDK中的java.beans.Introspector类的用途是发现Java类是否符合JavaBean规范 
 \* @see 如果有的框架或程序用到了Introspector类,那么就会启用一个系统级别的缓存,此缓存会存放一些曾加载并分析过的JavaBean的引用 
 \* @see 当Web服务器关闭时,由于此缓存中存放着这些JavaBean的引用,所以垃圾回收器无法回收Web容器中的JavaBean对象,最后导致内存变大 
 \* @see 而org.springframework.web.util.IntrospectorCleanupListener就是专门用来处理Introspector内存泄漏问题的辅助类 
 \* @see IntrospectorCleanupListener会在Web服务器停止时清理Introspector缓存,使那些Javabean能被垃圾回收器正确回收 
 \* @see ------------------------------------------------------------------------------------------------------------------- 
 \* @see Spring自身不会出现这种问题 
 \* @see 因为Spring在加载并分析完一个类之后会马上刷新JavaBeans Introspector缓存,这就保证Spring中不会出现这种内存泄漏的问题 
 \* @see 但有些程序和框架在使用了JavaBeans Introspector之后,没有进行清理工作(如Quartz,Struts),最后导致内存泄漏 
 \* @see ------------------------------------------------------------------------------------------------------------------- 
 \* @create Sep 24, 2013 9:10:09 PM 
 \* @author 玄玉<http://blog.csdn.net/jadyer>

\---------------------   
作者：玄玉   
来源：CSDN   
原文：https://blog.csdn.net/jadyer/article/details/11991457   
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