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.
Here's one thing that doesn't work. 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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