Add support for Resource Tracking to the DataFileProvider infrastructure
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Key: STANBOL-374
URL: https://issues.apache.org/jira/browse/STANBOL-374
Project: Stanbol
Issue Type: New Feature
Components: Commons
Reporter: Rupert Westenthaler
Assignee: Rupert Westenthaler
Currently the DataFileProvider only supports requests for resources. If a
specific resource is available the caller gets an InputStream for that
Resource. Otherwise a IOException is thrown.
Here the proposal is to add an new ResourceTracker Service that allows to
register/unregister ResourceListener instances
@Service
ResourceTracker
/** adds an listener for a resource with that name and a bundle **/
+ void add(ResourceListener listener, String bundleSymbolicName, String
name)
/** adds an listener for a resource with a given name **/
+ void add(ResourceListener listener, String name)
/** removes all resources for that specific listener instance. Useful
if the listening components gets deactivated. **/
+ void removeAll(ResourceListener listener)
/** removes listening to that the resource with that name/bundle for
that listener **/
+ void remove(ResourceListener listener, String bundleSymbolicName,
String name)
/** removes listening to that resource for that listener **/
+ void remove(ResourceListener listener, String name)
ResourceListener (interface)
/** Called as soon as a resource gets available. Also called for newly
registered
* resources if the requested resource is already present at the time
of registration
* @param resource the name of the available resource
* @param is the inputstream for that resource
* @return If <code>true</code> the registration for this event is
automatically removed.
* Otherwise the registration is kept and can be used to track if the
resource get unavailable.
**/
+ boolean available(String resource, InputStream is)
/** Called as soon as a previous available resource is no longer
available
* @param resource The name of the unavailable resource
* @return If <code>true</code> the registration for this event is
automatically removed.
* Otherwise the component receiving this call needs to remove the
registration them self.
**/
+boolean unavailable(String resource)
Implementation:
The suggestion is to
* add this to the "org.apache.stanbol.commons.stanboltools.datafileprovider"
bundle
* add the "ResourceTracker" and "ResourceListener" interface to the
"org.apache.stanbol.commons.stanboltools.datafileprovider" package
* add the implementation directly to the
"org.apache.stanbol.commons.stanboltools.datafileprovider.impl.MainDataFileProvider"
* use an own Thread that calls "getInputStream(...)" for all registered
resources in fixed intervals (e.g. 5sec) . Computational overhead for the
periodical polls should be minimal.
* The poll interval should a configurable.
Intended Usage:
* Initially I require this feature to listen for archived Solr indexes copied
to the /datafiles folders. Currently users need to manually restart the
Component that manages SolrIndexes after the according file is available.
* This feature will also be handy if we implement a functionality that allows
to download referenced datafiles via the web, because as soon as the downloads
completes the components depending on a resource could be notified.
* This feature could also optionally be used to deactivate functionality by
deleting the corresponding datafiles form the /datafiles folder. (e.g. the
OpenNLP component loads Language models via the DatafileProvider. Currently the
are kept in Memory even if the corresponding DataFile is no longer available.
Even if the user provides an updated version. The old version is still
available (in-memory) and the new one is only used after a restart of the
Stanbol environment. This feature would allow to get notified as soon as a
model is deleted and would trigger an re-initialisation of the model as soon as
the updated datafile is available again.
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