Hi Bart Perhaps this would be a good one for someone from the ASF to provide more details.
>From my point of view, if a resource provider is in fact providing a resource, >be it via listChildren or getResource, it must be the sole source of that >resource, i.e. no other resource provider must have resolved these resources >as this would essentially break the architecture, in which resource provider >hierarchies are managed by sling, not the providers themselves and there is a >1:1 relationship between resources and their providers. The fact calling resourceResolver.getResource(path); ends up in your resource provider is coincidental in this context, for it could be any other resource provider at runtime. The rule basically is that the resource and it's meta data must be new when returned by your provider. Kind regards, Olaf -----Original Message----- From: Bart Wulteputte [mailto:bart.wultepu...@gmail.com] Sent: Freitag, 9. Juni 2017 09:36 To: users@sling.apache.org Subject: Re: Resource provided by custom ResourceProvider crashes upon calling hasChildren() Hi Olaf, I'd like to dive into your last comment some further. "You can never re-provide a resource resolved by a different resource provider". In my case, I don't think I'm re-providing, I'm just providing - if anything, I'm delegating to the resource resolving mechanism which ends up at my ResourceProvider. So I'm not ending up at a different resource provider at this point, but actually the same resource provider. It's still not entirely clear to me conceptually speaking why this is a bad practise. Best regards 2017-06-08 23:34 GMT+02:00 Olaf <o...@x100.de>: > Hi Bart, > > I put them right in the code, where they are probably hard to spot :-) > > The essential one should be the one next to the place where you add > the resource to the list of resource in ResourceProvider#listChildren. > Updated > version: > > You can never re-provide a resource resolved by a different resource > provider: A resource has resource meta-data containing, amongst > others, the resolution path. Also, a resource is always tied to its > resource resolver via resource#getResourceProvider(). Thus, you must > create a new > (Synthetic) > resource here and add it to the list. For instance, you could extend > SyntheticResource to create your own resource wrapper, and delegate > Resource#adaptTo to your wrapped resource. > > > Kind regards, > Olaf > > -----Original Message----- > From: Bart Wulteputte [mailto:bart.wultepu...@gmail.com] > Sent: Donnerstag, 8. Juni 2017 23:31 > To: users@sling.apache.org > Subject: Re: Resource provided by custom ResourceProvider crashes upon > calling hasChildren() > > Hi Olaf, > > Is it possible that you didn't send your remarks? I don't see them in > your first mail. > > Best regards > > > _____________________________ > From: Olaf <o...@x100.de<mailto:o...@x100.de>> > Sent: donderdag, juni 8, 2017 11:25 PM > Subject: RE: Resource provided by custom ResourceProvider crashes upon > calling hasChildren() > To: <users@sling.apache.org<mailto:users@sling.apache.org>> > > > Hi Bart, > > I just saw you already used ResourceProvider#(ResolveContext ctx, > Resource parent), excellent. Forget my first remark then, providing a > SyntheticResource should do. > > Cheers, > Olaf > > -----Original Message----- > From: Olaf [mailto:o...@x100.de] > Sent: Donnerstag, 8. Juni 2017 23:23 > To: users@sling.apache.org<mailto:users@sling.apache.org> > Subject: RE: Resource provided by custom ResourceProvider crashes upon > calling hasChildren() > > Hi Bart! > > Resource providers are mighty, but tricky things indeed. Please find > my > >remarks below. > > Cheers, > Olaf > > -----Original Message----- > From: Bart Wulteputte [mailto:bart.wultepu...@gmail.com] > Sent: Donnerstag, 8. Juni 2017 22:50 > To: users@sling.apache.org<mailto:users@sling.apache.org> > Subject: Resource provided by custom ResourceProvider crashes upon > calling > hasChildren() > > Hi, > > While trying to implement a POC and I ran into a strange error, and I > hope you guys can help identify whether this is a bug, or if I'm just > doing something wrong. > > I'm playing around with custom resource providers to pull external > data into sling. I don't do anything crazy in there (yet), but it's > just as a poc. I want to combine it with custom resource > implementations as well. > > My resource provider is registered on path "/content/data" and > basically handles anything on this path. Currently I'm just building a > virtual data structure. Inside this virtual structure some paths will > have a very specific ResourceProvider implementation tied to said path > which retrieve the resource info from an external system when calling > listChildren. So for example "/content/data/2001/external/app" could > have a more specific resource provider registered here (which should > work based on provider priority). Unfortunately, I can't seem to get > part 1 (building the virtual > structure) working without some hacks. > > *My resource provider implementation looks like this:* > > @Override > public Resource getResource(@Nonnull final ResolveContext > resolveContext, @Nonnull final String path, @Nonnull final > ResourceContext resourceContext, final Resource parent) { return new > SyntheticResource(resolveContext.getResourceResolver(), > path, SyntheticResource.RESOURCE_TYPE_NON_EXISTING); > } > > > > Resources must never provide their own children - this is the > > resource > provider's responsibility, see ResourceProvider#listChildren( > ResolveContext ctx, Resource parent). The reason is that resource > providers can be nested, i.e. the child of a resource may be provided > by a different resource provider. Thus, the code below should be > situated in the before mentioned method of your resource provider. > > @Override > public Iterator<Resource> listChildren(@Nonnull final ResolveContext > resolveContext, @Nonnull final Resource resource) { final > ResourceResolver resourceResolver = > resolveContext.getResourceResolver(); > final List<Resource> list = new ArrayList<>(); // search data > basically returns a list of child paths // e.g. /content/data/2000, > /content/data/2001, ... > // since these are 'children' the resolving ends up in this > ResourceProvider // which yields a new SyntheticResource on the given > path (for now) for (String path : searchData.childrenOf(resource)) { > final Resource childRes = resourceResolver.getResource(path); > if (childRes != null) { > > > > You can never re-provide a resolved resource: A resource has > > resource > meta-data containing, amongst others, the resolution path. Also, a > resource is always tied to its resource resolver via > resource#getResourceProvider() . > Thus, you must create a new (Synthetic) resource here and add it to > the list. For instance, you could extend SyntheticResource to create > your own resource wrapper, and delegate Resource#adaptTo to your wrapped > resource. > > list.add(childRes); > } > } > return list.isEmpty() ? null : list.iterator(); } > > > > *The code producing my error:* > > Resource r=resourceResolver.getResource("/content/data"); > r.hasChildren(); > > > *My Error:* > > java.lang.UnsupportedOperationException: ResourceMetadata is locked at > org.apache.sling.api.resource.ResourceMetadata. > checkReadOnly(ResourceMetadat > a.java:367) > at > org.apache.sling.api.resource.ResourceMetadata.put( > ResourceMetadata.java:379 > ) > at > org.apache.sling.api.resource.ResourceMetadata. > setResolutionPath(ResourceMet > adata.java:276) > at > org.apache.sling.resourceresolver.impl.helper. > UniqueResourceIterator.seek(Un > iqueResourceIterator.java:51) > at > org.apache.sling.resourceresolver.impl.helper. > UniqueResourceIterator.seek(Un > iqueResourceIterator.java:30) > at > org.apache.sling.resourceresolver.impl.helper. > AbstractIterator.hasNext(Abstr > actIterator.java:33) > at > org.apache.sling.resourceresolver.impl.helper. > ResourceIteratorDecorator.hasN > ext(ResourceIteratorDecorator.java:45) > ... > > > *My analysis so far:* > > Because I use resourceResolver.getResource() inside the listChildren > method of my custom resource provider, I pass through some internal > resolving which do some decorating on the resource and the iterators. > This in itself is not a problem, but one of those decorators (the > ResourceDecoratorTracker) locks the ResourceMedatadata object - which > is a problem as other decorators like ResourceIteratorDecorator try to > update data (in this case it tries to set/update the resolutionPath of > the fetched resource's ResourceMetadata to the path of said resource > during the execution of 'next()' - which seems a tad odd). And here we > end up trying to modify a locked object. > > > This feels like a bug. I can get around it by creating my own > ResourceMetadata class which extends ResourceMetadata and overrides > the > lock() method to do nothing and passing that to the SyntheticResource > upon creation. But this feels like hacking. Second option: I don't use > the resourceResolver to get the resource, but instead create new > SyntheticResource objects in the listChildren of my ResourceProvider > directly (in the same way i would do 'getResource'). > > Preferably I want to pass through the appropriate ResourceProvider > (since the intend is to have more specific resource providers mounted > on paths inside this virtual structure). In theory this should work, > and in practise it does as well (if I hack it a bit as described before). > > So the main question is, can I do this in a non hackish way? And is > this a bug? > > > > > >
