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https://issues.apache.org/jira/browse/WICKET-2690?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12802345#action_12802345
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Kirill commented on WICKET-2690:
--------------------------------
Nice guess, but no. I couldn't find a reduced test case. I didn't say the issue
was an easy one, that I didn't.
> Stateless components and classloading
> --------------------------------------
>
> Key: WICKET-2690
> URL: https://issues.apache.org/jira/browse/WICKET-2690
> Project: Wicket
> Issue Type: Bug
> Components: wicket
> Affects Versions: 1.4.5
> Reporter: Kirill
>
> Following a post on the user list, which so far got no reply, posting the
> issue here:
> Wicket 1.4.5 with Tomcat 6.0.
> I'm trying to make a session-resistant (but *not* bookmarkable) link on the
> homepage that should work no matter if the page exists. If the page doesn't
> exist, I want it to be created and then the link event handler invoked. As
> far as I understand, StatelessLink should work for this purpose. However, I
> can't get it to work. From time to time, clicking it produces the following
> error in the console:
> SEVERE: unable to find listener interface ILinkListener
> org.apache.wicket.WicketRuntimeException: unable to find listener interface
> ILinkListener
> at
> org.apache.wicket.request.target.component.BookmarkableListenerInterfaceRequestTarget.processEvents(BookmarkableListenerInterfaceRequestTarget.java:159)
> at
> org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:92)
> at
> org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1250)
> at org.apache.wicket.RequestCycle.step(RequestCycle.java:1329)
> at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1428)
> at org.apache.wicket.RequestCycle.request(RequestCycle.java:545)
> at
> org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:479)
> at
> org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:312)
> at
> org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
> at
> org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
> at
> org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:390)
> at
> org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
> at
> org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
> at
> org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
> at
> org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
> at
> org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
> at
> org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
> at
> org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
> at
> org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
> at
> org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849)
> at
> org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
> at
> org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:454)
> at java.lang.Thread.run(Thread.java:619)
> Sometimes I also get the following (seemingly related) error:
> org.apache.wicket.protocol.http.request.InvalidUrlException:
> org.apache.wicket.WicketRuntimeException: Unable to instantiate Page class:
> com.my.HomePage. See below for details.
> at
> org.apache.wicket.protocol.http.WebRequestCycleProcessor.resolve(WebRequestCycleProcessor.java:262)
> at org.apache.wicket.RequestCycle.step(RequestCycle.java:1310)
> at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1428)
> at org.apache.wicket.RequestCycle.request(RequestCycle.java:545)
> at
> org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:479)
> at
> org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:312)
> at
> org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
> at
> org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
> at
> org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:390)
> at
> org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
> at
> org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
> at
> org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
> at
> org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
> at
> org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
> at
> org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
> at
> org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
> at
> org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
> at
> org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849)
> at
> org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
> at
> org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:454)
> at java.lang.Thread.run(Thread.java:619)
> Caused by: org.apache.wicket.WicketRuntimeException: Unable to instantiate
> Page class: com.my.HomePage. See below for details.
> at
> org.apache.wicket.request.AbstractRequestCycleProcessor.resolveBookmarkablePage(AbstractRequestCycleProcessor.java:286)
> at
> org.apache.wicket.protocol.http.WebRequestCycleProcessor.resolve(WebRequestCycleProcessor.java:78)
> ... 20 more
> Caused by: org.apache.wicket.WicketRuntimeException: Attempt to access
> unknown request listener interface ILinkListener
> at
> org.apache.wicket.request.AbstractRequestCycleProcessor.resolveListenerInterfaceTarget(AbstractRequestCycleProcessor.java:407)
> at
> org.apache.wicket.request.AbstractRequestCycleProcessor.resolveBookmarkablePage(AbstractRequestCycleProcessor.java:266)
> ... 21 more
> A reliable way to reproduce it is:
> 1) open the home page in the browser
> 2) restart the web application in Tomcat
> 3) click the link
> Every time I perform the above steps, I either get the first exception, or
> the second.
> It doesn't necessarily happen immediately when the session expires (but
> AFAICT it always happens some time after that). Looks like it happens when a
> classloader cache in the servlet container gets garbage-collected.
> I find the first stack trace especially interesting. I have traced the
> execution flow in debugger, and I'm confident that the first exception always
> happens after some Links get instantiated, and because Link implements
> ILinkListener, at that point the RequestListenerInterface instance for
> ILinkListener exists. However, RequestListenerInterface.register() method
> doesn't get called during the "resolve" step, so I must conclude that the
> servlet container uses the preexisting class at that point. But when the
> execution flow reaches AbstractRequestCycleProcessor.java:92 during the
> "process" step, the RequestListenerInterface instance for ILinkListener can
> no longer be found.
> Such inconsistencies happen when one class (AbstractRequestCycleProcessor?)
> is created by a different classloader than another class
> (RequestListenerInterface?).
> What remains unclear is why I can't see other reports of the same problem on
> the list. Am I doing something wrong?
> From what I know about servlet containers, you are not supposed to mess with
> classloading there. I did some of that in past, and it can be VERY hard to
> make it work across the implementations.
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