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| <h1 class="title">ARQ - The java: URI scheme</h1> |
| |
| |
| <main class="d-flex flex-xl-row flex-column"> |
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| <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="#dynamic-code-loading">Dynamic Code Loading</a></li> |
| <li><a href="#remapping">Remapping</a></li> |
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| <article class="flex-column me-lg-4"> |
| <p>ARQ uses URIs of the form <code><java:<i>package.class</i>></code> to provide |
| dynamic loading of code for |
| <a href="extension.html#valueFunctions">value functions</a> and |
| <a href="extension.html#propertyFunctions">property functions</a>. ARQ loads |
| the class when needed. For functions and property functions, it |
| also wraps it in the necessary factory code. A new instance of the |
| function or property function is created for each mention of the |
| name in each query.</p> |
| <h2 id="dynamic-code-loading">Dynamic Code Loading</h2> |
| <p>Any classes loaded by ARQ must already be on the java classpath. |
| ARQ does not create any new class loaders, nor modify the Java |
| class path in any way. The class path must be set up to include any |
| class files or jar files for dynamically loaded code.</p> |
| <p>Classes can be mor conveniently named in queries using SPARQL |
| <code>PREFIX</code>es but because dots can’t appear in the local part of a |
| prefixed name, all the package name and the final dot must be in |
| the <code>PREFIX</code> declaration.</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-sparql" data-lang="sparql"><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">PREFIX</span> <span style="color:#00f;font-weight:bold">fn</span>: <span style="color:#a0a000"><java:org.example.functions.></span> <span style="color:#080;font-style:italic"># Including the final dot</span> |
| </span></span><span style="display:flex;"><span>... |
| </span></span><span style="display:flex;"><span> <span style="color:#a2f;font-weight:bold">FILTER</span> <span style="color:#00f;font-weight:bold">fn</span>:<span style="color:#008000;font-weight:bold">alter</span>(<span style="color:#b8860b">?x</span>) |
| </span></span><span style="display:flex;"><span>... |
| </span></span></code></pre></div><h2 id="remapping">Remapping</h2> |
| <p>All code loading is performed via the <code>MappedLoader</code> class. Before |
| actually loading the code, the mapped loader applies any |
| transformation of URIs. For example, the ARQ function library has a |
| namespace of <code><http://jena.apache.org/ARQ/function#></code> and resides |
| in the Java package org.apache.jena.sparql.function.library. The |
| mapped loader includes a partial rewrite rule turning http URLs |
| starting with that namespace into java: URIs using the package |
| name.</p> |
| |
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| <li><a href="#remapping">Remapping</a></li> |
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