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https://issues.apache.org/jira/browse/TAPESTRY-1776?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12530115
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Ognen Ivanovski commented on TAPESTRY-1776:
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Yes, the errors can be avoided but I think Tapestry should not allow them to
happen. Allowing component/page classes to be loaded in by a classloader other
than the one intended is not a good idea.
It is especially annoying when such a thing happens within the "controlled"
environment of another page/component.
public class Referee {} /* component */
public class Referrer {
@Parameter(defaultPrefix="component")
private Referee reference; // this is trouble!
}
I would suggest that Tapestry installs a special class loader as the thread's
context classloader early in the request handling chain (probably as early as
possible).
This one would have two delegating classloaders
- the PackageAwareLoader, to which it delegates all loadClass() calls for
components and pages
- the orginal context class loader for all other classes
I think in this way component classes are still defined by the
PackageAwareLoader, so the cache can be flushed and at the same time you
inhibit classlading of unenhanced component / page classes.
> Component Class object exists in several instances
> ----------------------------------------------------
>
> Key: TAPESTRY-1776
> URL: https://issues.apache.org/jira/browse/TAPESTRY-1776
> Project: Tapestry
> Issue Type: Bug
> Components: tapestry-core
> Affects Versions: 5.0.5
> Environment: Mac OS X, Eclipse 3.3, Jetty Launcher, Jetty 5
> Reporter: Ognen Ivanovski
> Attachments: log.txt
>
>
> I get the following exception:
> java.lang.IllegalArgumentException: Could not find a coercion from type
> com.telekurs.pass.online.permissiongui.components.CheckboxGroup to type
> com.telekurs.pass.online.permissiongui.components.CheckboxGroup. Available
> coercions:... (full trace attached)
> Note that it says "cannot find a coercion from A to A". I did some debugging
> and indeed the class CheckboxGroup was represented by two different objects.
> Tapestry should not allow for a component class to be loaded differently than
> in the modified version.
> More details:
> - CheckBoxGroup is a component very similar to RadioGroup (80% code similar)
> it is used to group render a set of checkboxes with the same name.
> - BulkSelect is a js component that i used for "select all" and "select none"
> operations in connection to the CheckBoxGroup. It has a
> @Parameter(required = true, defaultPrefix="component")
> private CheckboxGroup checkboxes;
> They are used in the following way:
> <t:BulkSelect checkboxes="permissionSelections" select="true" />
> <t:CheckboxGroup t:id="permissionSelections"
> value="selected" encoder="permissionValueEncoder" disabled="disabled">
> <!-- ...-->
> </t:CheckboxGroup>
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