Thomas Watson created ARIES-1227:
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Summary: Allow PerserService to parse successfully when namespace
handlers are missing
Key: ARIES-1227
URL: https://issues.apache.org/jira/browse/ARIES-1227
Project: Aries
Issue Type: Improvement
Components: Blueprint
Reporter: Thomas Watson
Assignee: Thomas Watson
The blueprint ParserService exposes the blueprint parser to other bundles.
This is great because it allows other bundles to model and reason about
blueprint dependencies. But the ParserService currently fails with a
ComponentDefinitionException if a custom NamespaceHandler is used within the
component XML file being parsed and that custom NamespaceHandler service is not
currently registered.
This becomes painful in scenarios where we are trying to reason about the
dependencies of a group of bundles and one of these bundles provides a
NamespaceHandler service which will be used at runtime by other bundles in the
group. For example, an OSGi Subsystem may be installed with such a group of
bundles as its content. The subsystems implementation in Aries attempts to
model the blueprint dependencies of the bundle resources before actually
installing and starting the bundles. This is done by using the blueprint
ParserService. But it always fails to do so because any blueprint XML that
uses the custom namespace will fail to model correctly which ultimately results
in a subsystem installation failure.
It would be nice if the ParserService could be configured to ignore the missing
NamespaceHandlers and continue with modelling the basic blueprint XML. One way
to accomplish this would be to have a framework property that can be configured
to ignore when a namespace is missing while using the ParserService. This will
only change the behavior of the ParserService and not the internal usage of the
Parser implementation by blueprint-core. It should also not change the current
behavior of the ParserService unless the option to ignore is enabled explicitly.
Another option is to change the ParserService API somehow to pass in an option
to ignore unknown NamespaceHandlers. This has an unfortunate side-effect of
exploding the API of the ParserService and the many other layers built on top
of it (e.g. ParserProxy and ModelledResourceManager which get used by Aries
subsystesms). Perhaps that is the correct thing to do, but I am not
comfortable changing that much API for this usecase. A global switch that
simply enables the option to ignore missing NamespaceHandlers is good enough
for my usage. If others want to add API to allow clients of the API to make
that choice that is fine with me, but I would prefer that to be done by someone
more familiar with the overall API here.
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