Implement helper classloader
----------------------------
Key: SLING-1007
URL: https://issues.apache.org/jira/browse/SLING-1007
Project: Sling
Issue Type: New Feature
Components: Commons OSGi
Affects Versions: Commons OSGi 2.0.4
Reporter: Felix Meschberger
Currently we require the ScriptEngine[Factory] implementation bundles to create
bundle header
DynamicImport-Package: *
to be able to access anything from the scripts since scripts are executed in
the class loader of the script engine bundle.
The downside of running the scripts in the class loader of the script engine
bundle and using this global dynamic import are:
* scripts see internal classes of the script engine bundle
* scripts engine bundles must provide for classes for the scripts
* whenever a wire has been created for a script and the providing bundle is
updated or uninstalled, the script engine bundle is also cycled.
A better approach might be to provide a ClassLoader implementation which behind
the scenes manages access to packages exported by the bundles installed in the
system. I would imagine such an implementation along the following lines:
* Uses PackageAdmin to find a bundle providing the required class
* Copes with bundles being updated or uninstalled
Maybe coping with bundles being updated or uninstalled requires a two level
approach: a fronend class loader which answers the class and resource accesses
by relaying to a backend class loader. The back end classloader does the
hardwork of loading classes and resources by querying bundles. Whenever a
bundle is updated or uninstalled the backend classloader gets replaced. A
similar approach has been chosen for the Repository ClassLoader in the
jcr/classloader bundle.
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