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https://issues.apache.org/jira/browse/WICKET-6600?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16675031#comment-16675031
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Sven Meier commented on WICKET-6600:
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Sorry I've got sidetracked.
Yes, this problem is now warned about only. I've removed the stacktrace too,
since I don't find it that useful at that location any more.
Thanks.
> Error logging in AjaxRequestHandler is too strict
> -------------------------------------------------
>
> Key: WICKET-6600
> URL: https://issues.apache.org/jira/browse/WICKET-6600
> Project: Wicket
> Issue Type: Improvement
> Components: wicket-core
> Affects Versions: 8.0.0
> Reporter: Gert-Jan Schouten
> Assignee: Sven Meier
> Priority: Major
> Fix For: 8.2.0, 9.0.0
>
>
> As a result of these three commits:
> *
> [https://github.com/apache/wicket/commit/dec1293da853357f483eadec4616c9758ea025f9#diff-8964e43671328bf6f9b1d75703103db8]
> *
> [https://github.com/apache/wicket/commit/3be55cf5a24982cfca400225aabb6c4296859a7d#diff-8964e43671328bf6f9b1d75703103db8]
> *
> [https://github.com/apache/wicket/commit/830fb15c333ad6099f466b2344a84b513690db86#diff-8964e43671328bf6f9b1d75703103db8]
> Wicket now logs a stacktrace on error level if you add something to the
> AjaxRequestTarget that has been removed from the page. I don't think this is
> a good idea, because you're not always in control of what happens in an Ajax
> call. Imagine, for example, the following scenario:
> {code:java}
> public abstract class MyPanel extends Panel {
> public MyPanel(String id) {
> super(id);
> this.setOutputMarkupId(true);
> this.add(new AjaxLink("myLink") {
> public void onClick(final AjaxRequestTarget target) {
> this.executeImportantWork(target);
> //Display something nice on this Panel
> //...
> target.add(MyPanel.this); //In order to show the nice things
> }
> });
> }
> protected abstract void executeImportantWork(AjaxRequestTarget target);
> }
> {code}
> Now, what if the user of MyPanel actually adds an instance of MyPanel to the
> Page and then, in executeImportantWork, removes it and replaces it with smth
> else? Then, you get an error in the log, everytime someone clicks myLink.
> In this case, it could be fixed by adding MyPanel.this to the target *before*
> calling executeImportantWork, in which case you also get something in the
> log, but without stacktrace and on WARN level, namely this: "Component not
> rendered because it was already removed from page", but this is far less
> invasive than the scary stacktrace on ERROR level.
> In other cases, however, it may be more difficult to fix, for example when
> you're not in control of the source code of MyPanel. Sure, one could argue
> that you shouldn't alter the page hierarchy in the executeImportantWork
> method, but usually, there's always a certain edge case where 99% of the
> times, no page hierarchy change occurs, but that 1% of the times, it is
> necessary.
> Wicket is a component based framework, so it should be possible to specify
> components with abstract behaviour and not restrict the user of those
> components in what they can do in the implementation of that abstract
> behaviour, especially since, in this case, it does not lead to any actual
> problems and can safely be ignored with a warning.
> I suggest changing the level of the message to WARN and removing the
> stacktrace.
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