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| <h1 class="title">Working with RDF Streams in Apache Jena</h1> |
| |
| |
| <main class="d-flex flex-xl-row flex-column"> |
| |
| <aside class="text-muted align-self-start mb-3 p-0 d-xl-none d-block"> |
| <h2 class="h6 sticky-top m-0 p-2 bg-body-tertiary">On this page</h2> |
| <nav id="TableOfContents"> |
| <ul> |
| <li><a href="#streamrdf">StreamRDF</a></li> |
| <li><a href="#reading-data">Reading data</a></li> |
| <li><a href="#writing-data">Writing data</a></li> |
| <li><a href="#rdfformat-and-lang">RDFFormat and Lang</a></li> |
| </ul> |
| </nav> |
| </aside> |
| <article class="flex-column me-lg-4"> |
| <p>Jena has operations useful in processing RDF in a streaming |
| fashion. Streaming can be used for manipulating RDF at scale. Jena |
| provides high performance readers and writers for all standard RDF formats, |
| and it can be extended with custom formats.</p> |
| <p>The <a href="rdf-binary.html">RDF Binary</a> provides the highest |
| input parsing performance. N-Triples/N-Quads provide the highest |
| input parsing performance using W3C Standards.</p> |
| <p>Files ending in <code>.gz</code> are assumed to be gzip-compressed. Input and output |
| to such files takes this into account, including looking for the other file |
| extension. <code>data.nt.gz</code> is parsed as a gzip-compressed N-Triples file.</p> |
| <p>Jena does not support all possible compression formats itself, only |
| GZip and BZip2 are supported directly. If you want to use an |
| alternative compression format you can do so by adding suitable dependencies |
| into your project and passing an appropriate <code>InputStream</code>/<code>OutputStream</code> |
| implementation to Jena code e.g.</p> |
| <pre><code>InputStream input = new ZstdCompressorInputStream(....); |
| Graph graph = RDFParser.source(input).lang(Lang.NQ).toGraph(); |
| </code></pre> |
| <h2 id="streamrdf">StreamRDF</h2> |
| <p>The central abstraction is |
| <a href="/documentation/javadoc/arq/org.apache.jena.arq/org/apache/jena/riot/system/StreamRDF.html"><code>StreamRDF</code></a> |
| which is an interface for streamed RDF data. It covers triples and quads, |
| and also parser events for prefix settings and base URI declarations.</p> |
| <pre><code>public interface StreamRDF { |
| /** Start processing */ |
| public void start() ; |
| |
| /** Triple emitted */ |
| public void triple(Triple triple) ; |
| |
| /** Quad emitted */ |
| public void quad(Quad quad) ; |
| |
| /** base declaration seen */ |
| public void base(String base) ; |
| |
| /** prefix declaration seen */ |
| public void prefix(String prefix, String iri) ; |
| |
| /** Finish processing */ |
| public void finish() ; |
| } |
| </code></pre> |
| <p>There are utilities to help:</p> |
| <ul> |
| <li><a href="/documentation/javadoc/arq/org.apache.jena.arq/org/apache/jena/riot/system/StreamRDFLib.html"><code>StreamRDFLib</code></a> – create <code>StreamRDF</code> objects</li> |
| <li><a href="/documentation/javadoc/arq/org.apache.jena.arq/org/apache/jena/riot/system/StreamRDFOps.html"><code>StreamRDFOps</code></a> – helpers for sending RDF data to <code>StreamRDF</code> objects</li> |
| </ul> |
| <h2 id="reading-data">Reading data</h2> |
| <p>All parsers of RDF syntaxes provided by RIOT are streaming with the |
| exception of JSON-LD. A JSON object can have members in any order so the |
| parser may need the whole top-level object in order to have the information |
| needed for parsing.</p> |
| <p>The <a href="/documentation/javadoc/arq/org.apache.jena.arq/org/apache/jena/riot/RDFDataMgr.html#parse%28org.apache.jena.riot.system.StreamRDF%2C%20java.io.InputStream%2C%20org.apache.jena.riot.Lang%29"><code>parse</code> functions</a> |
| of <a href="/documentation/javadoc/arq/org.apache.jena.arq/org/apache/jena/riot/RDFDataMgr.html">RDFDataMgr</a> |
| directs the output of the parser to a <code>StreamRDF</code>. For example:</p> |
| <pre><code>StreamRDF destination = ... |
| RDFDataMgr.parse(destination, "http://example/data.ttl") ; |
| </code></pre> |
| <p>The above code reads the remote URL, with content negotiation, and sends the |
| triples to the <code>destination</code>.</p> |
| <h2 id="writing-data">Writing data</h2> |
| <p>Not all RDF formats are suitable for writing as a stream. Formats that |
| provide pretty printing (for example the default <code>RDFFormat</code> for each of |
| Turtle, TriG and RDF/XML) require analysis of the entire model in order |
| to determine nestable structures of blank nodes and for using specific |
| syntax for RDF lists.</p> |
| <p>These languages can be used for streaming output but with an appearance |
| that is necessarily “less pretty”. |
| See <a href="rdf-output.html#streamed-block-formats">“Streamed Block Formats”</a> |
| for details.</p> |
| <p>The <a href="/documentation/javadoc/arq/org.apache.jena.arq/org/apache/jena/riot/system/StreamRDFWriter.html"><code>StreamRDFWriter</code></a> |
| class has functions that write graphs and datasets |
| using a streaming writer and also provides for the creation of |
| an <code>StreamRDF</code> backed by a stream-based writer</p> |
| <pre><code>StreamRDFWriter.write(output, model.getGraph(), lang) ; |
| </code></pre> |
| <p>which can be done as:</p> |
| <pre><code>StreamRDF writer = StreamRDFWriter.getWriterStream(output, lang) ; |
| StreamRDFOps.graphToStream(model.getGraph(), writer) ; |
| </code></pre> |
| <p>N-Triples and N-Quads are always written as a stream.</p> |
| <h2 id="rdfformat-and-lang">RDFFormat and Lang</h2> |
| <table> |
| <thead> |
| <tr> |
| <th><a href="/documentation/javadoc/arq/org.apache.jena.arq/org/apache/jena/riot/RDFFormat.html">RDFFormat</a></th> |
| <th><a href="/documentation/javadoc/arq/org.apache.jena.arq/org/apache/jena/riot/Lang.html">Lang</a> shortcut</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td><code>RDFFormat.TURTLE_BLOCKS</code></td> |
| <td><code>Lang.TURTLE</code></td> |
| </tr> |
| <tr> |
| <td><code>RDFFormat.TURTLE_FLAT</code></td> |
| <td></td> |
| </tr> |
| <tr> |
| <td><code>RDFFormat.TRIG_BLOCKS</code></td> |
| <td><code>Lang.TRIG</code></td> |
| </tr> |
| <tr> |
| <td><code>RDFFormat.TRIG_FLAT</code></td> |
| <td></td> |
| </tr> |
| <tr> |
| <td><code>RDFFormat.NTRIPLES_UTF8</code></td> |
| <td><code>Lang.NTRIPLES</code></td> |
| </tr> |
| <tr> |
| <td><code>RDFFormat.NTRIPLES_ASCII</code></td> |
| <td></td> |
| </tr> |
| <tr> |
| <td><code>RDFFormat.NQUADS_UTF8</code></td> |
| <td><code>Lang.NQUADS</code></td> |
| </tr> |
| <tr> |
| <td><code>RDFFormat.NQUADS_ASCII</code></td> |
| <td></td> |
| </tr> |
| <tr> |
| <td><code>RDFFormat.TRIX</code></td> |
| <td><code>Lang.TRIX</code></td> |
| </tr> |
| <tr> |
| <td><code>RDFFormat.RDF_THRIFT</code></td> |
| <td><code>Lang.RDFTHRIFT</code></td> |
| </tr> |
| <tr> |
| <td><code>RDFFormat.RDF_PROTO</code></td> |
| <td><code>Lang.RDFPROTO</code></td> |
| </tr> |
| </tbody> |
| </table> |
| |
| </article> |
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| <h2 class="h6 sticky-top m-0 p-2 bg-body-tertiary">On this page</h2> |
| <nav id="TableOfContents"> |
| <ul> |
| <li><a href="#streamrdf">StreamRDF</a></li> |
| <li><a href="#reading-data">Reading data</a></li> |
| <li><a href="#writing-data">Writing data</a></li> |
| <li><a href="#rdfformat-and-lang">RDFFormat and Lang</a></li> |
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