org.springframework.web.util.IntrospectorCleanupListener的用途

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. * * <p><b>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!</b> This listener performs proper cleanup, * to allow for garbage collection to take effect. * * <p>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. * * <p>Note that this listener is <i>not</i> 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. * * <b>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).</b> * In such a scenario, this listener will properly clean up Spring's introspection cache. * * <p>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. * * <p>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! * * <p><b>This listener should be registered as the first one in <code>web.xml</code>, * before any application listeners such as Spring's ContextLoaderListener.</b> * 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> */