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https://issues.apache.org/jira/browse/CAMEL-21513?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Claus Ibsen updated CAMEL-21513:
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Fix Version/s: 4.x
> CoreTypeRegistry can create unpredictable type to converter mappings
> --------------------------------------------------------------------
>
> Key: CAMEL-21513
> URL: https://issues.apache.org/jira/browse/CAMEL-21513
> Project: Camel
> Issue Type: Improvement
> Components: camel-core
> Affects Versions: 4.4.4
> Reporter: Nathan
> Priority: Minor
> Fix For: 4.x
>
>
> *Context*
> The CoreTypeConverterRegistry uses a map of converters to find a converter
> for a TypeConvertible<from,to>.
> If there is no known converter it attempts to find one in the existing
> converter map based on the idea that an existing converter on a super class
> can be used.
> This logic is contained in the TypeResolverHelper.tryMatch method. The
> tryMatch method will do an exhaustive search on the types in the converter
> and the super classes of the to convert value.
> To do this tryMatch will iterate over all the existing converters. Each
> existing converter<from,to> will then be compared to the super classes of the
> TypeConvertible<from,to>.
> *Problem*
> The problem is that the TypeResolverHelper.tryMatch can be highly random in
> selecting a converter. The first converter that matches is chosen and stored
> for all future usage of this specific type conversion.
> But the order of iteration for the converter map is not guaranteed to be the
> same every time. It is very likely that it is different for every load, since
> it depends on the order that converters have been added and there is no order
> guarantee on HashMap entry set iteration.
> This is not only theoretical, we already had a problem with the type
> conversion of DeferredElementNSImpl to CxfPayload. DeferredElementNSImpl
> implements both org.w3c.dom.Element and org.w3c.dom.NodeList. Both of those
> have converters in the CxfPayloadConverterLoader.
> But the converter chosen was random and often changed after application
> restarts. This caused problems for us since the NodeList to CxfPayload did
> not transform the DeferredElementNSImpl as expected.
> *Workaround*
> There is an easy workaround by defining your own converters to ensure the
> correct conversion happens, but this workaround can be cumbersome for
> applications with a lot of implicit type conversions.
> Especially if the correct conversion does exist, but is just not used.
> *Solution?*
> I do think there is a potential solution, the converter iteration is random
> and it would be inefficient to order it. That would also not necessarily fix
> anything since any order could be wrong for some specific conversion.
> Instead the TypeResolverHelper.tryMatch could change things by iterating over
> the super classes of the from first. And try to find a converter for each
> super class.
> The complication is that the super class iteration is done in the
> TypeConvertible, so it would have to be duplicated or moved into the
> TypeResolverHelper to do that.
> The method getInterfaces that is used in the TypeConvertible is ordered by
> the JDK, so there would be no randomness. Instead it would select the first
> existing converter that is actually closest to the target class.
> This is much better than just the first converter that happens to match with
> an interface removed 5 super classes.
> For the DeferredElementNSImpl it would then go:
> look for DeferredElementNSImpl -> not found
> look for ElementNSImpl -> not found
> look for ElementImpl -> not found
> Look for Element -> found CxfPayloadConverter.elementToCxfPayload
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