Rupert Westenthaler created STANBOL-996:
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Summary: Seperate OSGI Services and Components for the Entityhub
Key: STANBOL-996
URL: https://issues.apache.org/jira/browse/STANBOL-996
Project: Stanbol
Issue Type: Bug
Components: Entityhub
Affects Versions: entityhub-0.11.0
Reporter: Rupert Westenthaler
Assignee: Rupert Westenthaler
Currently most Entityhub components are both OSGI services and components
(meaning that they have both the @Service and @Component annotation).
Affected:
* ReferencedSite
* Cache
* SolrYard
* ClerezzaYard
Not Affected:
* ManagedSite: This component uses already the described model
Why to separate @Component and @Service implementations
================================================
A detailed description of the design can be found in [1].
The main reason for adopting this model for the Entityhub is not to provide its
services outside of OSGI, but to solve the problem of registered services with
missing dependencies (e.g. A SolrYard that is still missing the configured
SolrServer).
The new model will allow to
* check in the activate method of the Component if the user provided
configuration is valid
* init and open serviceTracker for the referenced services
* mark the component as activated
but only as soon as all tracked services do become available the Service would
be instantiated and registered with the OSGI environment.
With this model Entityhub services (e.g. the RESTful API for a ReferencedSite)
would only become available if the site is ready to use. With the current
architecture this is the case as soon as the activate method of the component
completes. Because of this Users do get Exceptions like (example taken from [2])
java.lang.IllegalStateException: Unable to initialize the Cache with Yard
netzmuehleIndex!
This is usually caused by Errors while reading the Cache Configuration from
the Yard.
at
org.apache.stanbol.entityhub.core.site.CacheImpl.getCacheYard(CacheImpl.java:214)
[..]
Caused by: org.apache.stanbol.entityhub.servicesapi.yard.YardException:
TheSolrIndex
'netzmuehle' for SolrYard 'netzmuehle Index' is currently not active!
at
org.apache.stanbol.entityhub.yard.solr.impl.SolrYard.getServer(SolrYard.java:512)
[..]
Backward Compatibility
==================
The new design will require to add new '{service}Component' classes (e.g.
SolrYardComponent, ReferencedSiteComponent). Why those will take the same
configurations as the current {service}s OSGI would - by default - assume the
configuration files to be named after the Class name. This would mean that
current configuration files would no longer be considered by the new
'{service}Component's.
To avoid this and provide full backward compatibility the 'name' parameter of
the new '{service}Component's need to be set to the 'name' used of the old
{service} classes.
[1] http://markmail.org/thread/yw6l5pnk6djovcjy
[2] http://markmail.org/message/7etfzzhicsuh26m4
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