Julian Sedding created SLING-8269:
-------------------------------------
Summary: Generics in ResourceProvider SPI don't resolve
Key: SLING-8269
URL: https://issues.apache.org/jira/browse/SLING-8269
Project: Sling
Issue Type: Improvement
Components: API
Affects Versions: API 2.11.0
Reporter: Julian Sedding
In the "new" {{ResourceProvider}} SPI a resource provider always "owns" its
root. This means that below that path no other RP is asked for resources
(unless it's registered on a more specific root path). In order to allow for
the scenario where a RP falls back to \{{Resource}}s provided by other RPs, an
API was added, that I gather should be used as follows:
{code:java}
public Iterator<Resource> listChildren(ResolveContext<Whatever> ctx, Resource
parent) {
Iterator<Resource> ownChildren = ... // compute child resource
ResolveContext<?> parentCtx = ctx.getParentResolveContext();
ResourceProvider<?> parentProvider = ctx.getParentResourceProvider();
if (parentCtx == null || parentProvider == null) {
return null;
}
return parentProvider.listChildren(parentCtx, parent);
}
{code}
However, the {{parentCtx}} on the last line does not match the signature of
{{listChildren(ResourceContext<T>, Resource)}}, because the generic type of
both {{ResolveContext<?>}} and {{ResourceContext<T>}} (from the
{{listChildren}} method signature) do not match, leading to the following
compile-time error:
{noformat}
incompatible types:
org.apache.sling.spi.resource.provider.ResolveContext<capture#1 of ?> cannot be
converted to org.apache.sling.spi.resource.provider.ResolveContext<capture#2 of
?>
{noformat}
This can be worked around by dropping generic types of the local variables and
accepting an "unchecked type" warning, i.e.:
{code:java}
ResolveContext parentCtx = ctx.getParentResolveContext();
ResourceProvider parentProvider = ctx.getParentResourceProvider();
{code}
cc [~cziegeler]
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