增加方式如下：
<listener>
<listener-class>
org.springframework.web.util.IntrospectorCleanupListener
</listener-class>
</listener>
spring的說明如下：
Listener that flushes the JDK's JavaBeans Introspector
cache on web app shutdown. 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'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 web.xml,
before any application listeners such as Spring's ContextLoaderListener.
This allows the listener to take full effect at the right time of the lifecycle.
其中JavaBeans Introspector是一個類，位置在Java.bean.Introspector，這個類的用途是發現java類是否符合javaBean規范，也就是這個類是不是javabean。具體用法可以參照jdk文檔；
上面的意思就是，如果有的框架或者程序用到了JavaBeans Introspector了，那么就啟用了一個系統級別的緩存，這個緩存會存放一些曾加載并分析過的javabean的引用，當web服務器關閉的時候，由于這個緩存中存放著這些javabean的引用，所以垃圾回收器不能對web容器中的javaBean對象進行回收，導致內存越來越大。
spring提供的org.springframework.web.util.IntrospectorCleanupListener就解決了這個問題，他會在web服務器停止的時候，清理一下這個Introspector緩存。使那些javabean能被垃圾回收器正確回收。
spring不會出現這種問題，因為spring在加載并分析完一個類之后會馬上刷新JavaBeans Introspector緩存，這樣就保證了spring不會出現這種內存泄漏的問題。
但是有很多程序和框架在使用了JavaBeans Introspector之后，都沒有進行清理工作，比如quartz、struts；解決辦法很簡單，就是上面的那個配置。