The StreamManager is a utility to find and read files into models. There is a standard global StreamManager and applications may also define specific ones by constructing additional StreamManagers.
The LocationMapper provides alternative locations for RDF data.
The Stream Manager
Files are named by a string, according to the conventions of their storage system. Typically this is by URI. There are a number of storage system adapters provided:
- File locator (with own current directory)
- URL locator (HTTP and FTP)
- Class loader locator
- Zip file locator
The global stream manager has a file location, a URL locator and a class loader (tried in that order).
A StreamManager can have an associated LocationMapper that transforms names before use. This means local copies of documents can be used transparently to the rest of the application.
A StreamManager provides an “open” operation to get an
to the resource.
The LocationMapper configuration file
Location mapping files are RDF - they may be written in RDF/XML, Turtle
.ttl) or N-Triples (file suffix
.nt). The default
is RDF/XML unless one of these suffices is found.
@prefix lm: <http://jena.hpl.hp.com/2004/08/location-mapping#> .  lm:mapping [ lm:name "file:foo.ttl" ; lm:altName "file:etc/foo.ttl" ] , [ lm:prefix "file:etc/" ; lm:altPrefix "file:ETC/" ] , [ lm:name "file:etc/foo.ttl" ; lm:altName "file:DIR/foo.ttl" ] .
There are two types of location mapping: exact match renaming and prefix renaming. When trying to find an alternative location, a LocationMapper first tries for an exact match; if none is found, the LocationMapper will search for the longest matching prefix. If two are the same length, there is no guarantee on order tried; there is no implied order in a location mapper configuration file (it sets up two hash tables).
In the example above,
because that is an exact match. The prefix match of file:etc/ is
All string tests are done case sensitively because the primary use is for URLs.
- Property values are not URIs, but strings. This is a system feature, not an RDF feature. Prefix mapping is name rewriting; alternate names are not treated as equivalent resources in the rest of Jena. While application writers are encouraged to use URIs to identify files, this is not always possible.
- There is no check to see if the alternative system resource is equivalent to the original.
A LocationMapper finds its configuration file by looking for the following files, in order:
This is specified as a path - note the path separator is always the character ‘;’ regardless of operating system because URLs contain ‘:’.
Applications can also set mappings programmatically. No configuration file is necessary.
The base URI for reading models with the StreamManager will be the original URI, not the alternative location.
If log4j2, set the logging level of the classes:
logger.filemanager.name = org.apache.jena.riot.system.stream.StreamManager logger.filemanager.level = ALL logger.location-manager.name = org.apache.jena.riot.system.stream.LocationMapper logger.location-manager.level = ALL