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<h1 class="title">The Jena StreamManager and LocationMapper</h1>
<p>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.</p>
<p>The LocationMapper provides alternative locations for RDF data.</p>
<h2 id="the-stream-manager">The Stream Manager</h2>
<p>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:</p>
<ul>
<li>File locator (with own current directory)</li>
<li>URL locator (HTTP and FTP)</li>
<li>Class loader locator</li>
<li>Zip file locator</li>
</ul>
<p>The global stream manager has a file location, a URL locator and a
class loader (tried in that order).</p>
<p>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.</p>
<p>A StreamManager provides an &ldquo;open&rdquo; operation to get an <code>InputStream</code>
to the resource.</p>
<h2 id="the-locationmapper-configuration-file">The LocationMapper configuration file</h2>
<p>Location mapping files are RDF - they may be written in RDF/XML, Turtle
(file suffix <code>.ttl</code>) or N-Triples (file suffix <code>.nt</code>). The default
is RDF/XML unless one of these suffices is found.</p>
<pre><code>@prefix lm: &lt;http://jena.hpl.hp.com/2004/08/location-mapping#&gt; .
[] lm:mapping
[ lm:name &quot;file:foo.ttl&quot; ; lm:altName &quot;file:etc/foo.ttl&quot; ] ,
[ lm:prefix &quot;file:etc/&quot; ; lm:altPrefix &quot;file:ETC/&quot; ] ,
[ lm:name &quot;file:etc/foo.ttl&quot; ; lm:altName &quot;file:DIR/foo.ttl&quot; ]
.
</code></pre>
<p>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).</p>
<p>In the example above, <code>file:etc/foo.ttl</code> becomes <code>file:DIR/foo.ttl</code>
because that is an exact match. The prefix match of file:etc/ is
ignored.</p>
<p>All string tests are done case sensitively because the primary use
is for URLs.</p>
<p>Notes:</p>
<ul>
<li>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.</li>
<li>There is no check to see if the alternative system resource is
equivalent to the original.</li>
</ul>
<p>A LocationMapper finds its configuration file by looking for the
following files, in order:</p>
<ul>
<li><code>location-mapping.ttl</code></li>
<li><code>location-mapping.rdf</code></li>
<li><code>etc/location-mapping.rdf</code></li>
<li><code>etc/location-mapping.ttl</code></li>
</ul>
<p>This is specified as a path - note the path separator is always
the character &lsquo;;&rsquo; regardless of operating system because URLs
contain &lsquo;:'.</p>
<p><code>location-mapping.ttl;location-mapping.rdf;etc/location-mapping.rdf;etc/location-mapping.ttl</code></p>
<p>Applications can also set mappings programmatically.
No configuration file is necessary.</p>
<p>The base URI for reading models with the StreamManager will be the
original URI, not the alternative location.</p>
<h3 id="debugging">Debugging</h3>
<p>If log4j2, set the logging level of the classes:</p>
<pre><code>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
</code></pre>
<h3 id="see-also">See also</h3>
<p>Javadoc:</p>
<ul>
<li><a href="/documentation/javadoc/arq/org/apache/jena/riot/system/stream/StreamManager.html">StreamManager</a></li>
<li><a href="/documentation/javadoc/arq/org/apache/jena/riot/system/stream/LocationMapper.html">LocationMapper</a></li>
</ul>
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