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https://issues.apache.org/jira/browse/WICKET-625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12537612
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Alastair Maw commented on WICKET-625:
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If you keep references to class objects in static fields, the VM isn't capable
of deducing that this is a circular reference.
Method and Field objects internally reference their Class, so you can't hold on
to those, either. Equally, you can't put them in a HashMap that's a static
field, as it's obviously all the same problem.
You can easily Google for more information on this if you're not convinced.
See for example:
http://www.szegedi.org/articles/memleak.html
http://opensource.atlassian.com/confluence/spring/pages/viewpage.action?pageId=2669
etc.
> Wicket doesn't clean up properly when hot-deploying; hangs onto Class
> references.
> ---------------------------------------------------------------------------------
>
> Key: WICKET-625
> URL: https://issues.apache.org/jira/browse/WICKET-625
> Project: Wicket
> Issue Type: Bug
> Components: wicket, wicket-extensions, wicket-spring
> Affects Versions: 1.3.0-beta1
> Reporter: Alastair Maw
> Assignee: Alastair Maw
> Fix For: 1.3.0-beta5
>
> Attachments: WICKET-625.patch
>
>
> When you undeploy a webapp, ideally it should go away and its
> WebAppClassLoader should be garbage collected. There are various reasons this
> won't happen, but they essentially split into two problems:
> 1) The App Server has references to classes in the WebAppClassLoader in its
> own objects (on Tomcat these are typically commons logging statics in
> StandardContext in catalina, or some of the jakarta code). There's not much
> you can do about this, short of getting a better app server.
> 2) You hold references to Class objects loaded by your WebAppClassLoader in
> static fields in other Classes loaded by your WebAppClassLoader.
> Number 2 can be solved by the use of WeakReferences to the Class objects.
> Note that you also need to be careful about classes that have Class
> references internally, such as java.lang.reflect.Method and Field. You can
> also hold these items in a WeakReference, but they have the potential to be
> garbage collected randomly, unlike the underlying Class objects.
> I have some patches that allow me to start up and shut down a Spring-backed
> Wicket-based app and have the classloader cope properly. They could probably
> do with some review.
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