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https://issues.apache.org/jira/browse/WICKET-6600?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16663819#comment-16663819
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Sven Meier commented on WICKET-6600:
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Sorry, but this just doesn't look right: If we agree that adding these
components is an error (as indicated by the exception in development config),
then it should be logged as error in deployment config to be consistent.
I'd rather degrade this to a warning, always being logged independently from
the current config (including stacktrace). As you've pointed out, nothing
really bad happens when you try to update a component no longer in the page.
> 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
> Priority: Major
>
> 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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