Data File Provider
The DataFileProvider provides data files (InputStreams actually) to OSGi components.
Usage
Datafiles are requested by name. Optionally the symbolic name of the bundle
requesting the data file can be parsed. This allows to serve different versions
of the same data file to different bundles. In addition requesters can provide
a Map
Main DataFileProvider
The MainDataFileProvider is the default implementation of the DataFileProvider interface. It registers itself with a service.ranking of Integer.MAX_VALUE to make it the default provider. I also keeps a list of all the other DataFileProviders.
The main DataFileProvider ignores other providers if it finds the requested data file in the filesystem, in a specific folder ("datafiles folder"). The name of that folder is configurable in the main DataFileProvider service. The default value is "stanbol/datafiles".
If it can not find the requested file it forwards the request to all other active DataFileProvider instances sorted by service.ranking.
When a bundle with symbolic name foo asks for data file bar.bin, the main DataFileProvider first looks for a file named foo-bar.bin in the datafiles folder, then for a file named bar.bin. Only if both files could not be found the request is forwarded to the other registered DataFileProviders.
Providing DataFiles
Bundles may provide there own DataFileProvider service. This might be useful if they need to provide a default version for a data file, but intend to allow users to override this by copying an other version to the "datafiles folder" of the Main DataFileProvider.
It they provide such a DataFileProvider service it must register it in its Activator, so that it's up before any component of the bundle asks for it.
If the Bundle does not want to provide a file also to other bundles than it should check if the parsed bundleSymbolicName is equals to its own.
DataFileProvider for OSGI Bundles
Implemenation of a DataFileProvider that allows to load DataFiles from OSGI Bundles.
Apache Sling OSGI Installer
The OSGi installer is a central service for handling installs, updates and uninstall of "artifacts". By default, the installer supports bundles and configurations for the OSGi configuration admin. Apache Stanbol extends this by the possibility to install Solr indexes (see "org.apache.stanbol.commons.solr.install" for details).
Note: While the Sling OSGI Installer by default supports the installation of Bundles this extension allows to install resources provided by bundles.
Usage
This implementation tracks all Bundles of the OSGI Environment that define the "Data-Files" key. The value is interpreted as a comma separated list of paths to the folders that contain the data files.
For each Bundle that provides Data-Files an own DataFileProvider instance is registered if the Bundle is STARTED and ungegisterd as soon as the Bundle is STOPPED. The MainDataFileProvider keeps track of all active DataFileProviders.
In addition to the "Data-Files" key an optional "Data-Files-Priority" can be used to spefify the service-ranking for the DataFileProvider created for the configured folders within a Bundle. If a data file is provided by more than one DataFileProvider the one provided by the DataFileProvider with the higest Ranking will be returned. The default ranking is "0".
Data file names parsed to this DataFileProvider are interpreted as relative to all configured data file paths.
Defining Manifest keys with Maven
When using the maven-bundle-plugin the "Install-Path" header can be defined like this:
<plugin> <groupId>org.apache.felix</groupId> <artifactId>maven-bundle-plugin</artifactId> ... <configuration> <instructions> <Data-Files>data,extras/data</Data-Files> <Data-Files-Priority>-100</Data-Files-Priority> </instructions> </configuration> </plugin>
This would install all data files located within
data/ extras/data
and will register them with a priority of "-100".
OSGI Console Pligin
An OSGi console plugin lists all (successful or failed) requests to the main DataFileProvider service, along with their downloadExplanations. This list of requests can also be queried so that failed requests can be shown on the stanbol server home page, for example. This provides a single location where stanbol users see what data files are needed and which ones were actually loaded from where.
Data File Tracker
While the DataFileProvider only supports requests for resources the Tracker allows register DataFileListener for a specific DataFile.
If the requested DataFile becomes available or unavailable the listener is notified about the state.
Because the DataFileProvider does not natively support such events the tracker uses periodical requests for all tracked DataFiles.
Note that registered Listeners are not kept if the DataFileTracker service is restarted.