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Posted to commits@jena.apache.org by bu...@apache.org on 2015/09/19 14:04:01 UTC
svn commit: r966006 - in /websites/staging/jena/trunk/content: ./
documentation/notes/system-initialization.html
Author: buildbot
Date: Sat Sep 19 12:04:00 2015
New Revision: 966006
Log:
Staging update by buildbot for jena
Added:
websites/staging/jena/trunk/content/documentation/notes/system-initialization.html
Modified:
websites/staging/jena/trunk/content/ (props changed)
Propchange: websites/staging/jena/trunk/content/
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Added: websites/staging/jena/trunk/content/documentation/notes/system-initialization.html
==============================================================================
--- websites/staging/jena/trunk/content/documentation/notes/system-initialization.html (added)
+++ websites/staging/jena/trunk/content/documentation/notes/system-initialization.html Sat Sep 19 12:04:00 2015
@@ -0,0 +1,259 @@
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
+<html>
+<head>
+<!--
+
+ Licensed to the Apache Software Foundation (ASF) under one or more
+ contributor license agreements. See the NOTICE file distributed with
+ this work for additional information regarding copyright ownership.
+ The ASF licenses this file to You under the Apache License, Version 2.0
+ (the "License"); you may not use this file except in compliance with
+ the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE- 2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+-->
+
+ <title>Apache Jena - Apache Jena Initialization</title>
+ <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+ <meta name="viewport" content="width=device-width, initial-scale=1.0">
+
+ <link href="/css/bootstrap.min.css" rel="stylesheet" media="screen">
+ <link href="/css/bootstrap-extension.css" rel="stylesheet" type="text/css">
+ <link href="/css/jena.css" rel="stylesheet" type="text/css">
+ <link rel="shortcut icon" href="/images/favicon.ico" />
+
+ <script src="https://code.jquery.com/jquery-2.0.3.min.js"></script>
+ <script src="/js/jena-navigation.js" type="text/javascript"></script>
+ <script src="/js/bootstrap.min.js" type="text/javascript"></script>
+ <script src="/js/breadcrumbs.js" type="text/javascript"></script>
+
+ <script src="/js/improve.js" type="text/javascript"></script>
+
+
+ <!-- Uncomment to enable code coloring <link href="/css/codehilite.css" rel="stylesheet" type="text/css"> -->
+
+</head>
+
+<body>
+
+
+
+<nav class="navbar navbar-default" role="navigation">
+<div class="container">
+ <div class="navbar-header">
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+ <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-ex1-collapse">
+ <span class="icon-bar"></span>
+ <span class="icon-bar"></span>
+ <span class="icon-bar"></span>
+ </button>
+ <a class="navbar-brand" href="/index.html">
+ <img class="logo-menu" src="/images/jena-logo/jena-logo-notext-small.png" alt="jena logo">Apache Jena</a>
+ </div>
+
+ <div class="collapse navbar-collapse navbar-ex1-collapse">
+ <ul class="nav navbar-nav">
+ <li id="homepage"><a href="/index.html"><span class="glyphicon glyphicon-home"></span> Home</a></li>
+ <li id="download"><a href="/download/index.cgi"><span class="glyphicon glyphicon-download-alt"></span> Download</a></li>
+ <li class="dropdown">
+ <a href="#" class="dropdown-toggle" data-toggle="dropdown"><span class="glyphicon glyphicon-book"></span> Learn <b class="caret"></b></a>
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+ <li><a href="/documentation/query/manipulating_sparql_using_arq.html">Manipulating SPARQL using ARQ</a></li>
+ <li><a href="/tutorials/using_jena_with_eclipse.html">Using Jena with Eclipse</a></li>
+ <li><a href="/documentation/notes/index.html">How-To's</a></li>
+ <li class="divider"></li>
+ <li class="dropdown-header">References</li>
+ <li><a href="/documentation/index.html">Overview</a></li>
+ <li><a href="/documentation/javadoc/">Javadoc</a></li>
+ <li><a href="/documentation/rdf/index.html">RDF API</a></li>
+ <li><a href="/documentation/io/">RDF I/O</a></li>
+ <li><a href="/documentation/query/index.html">ARQ (SPARQL)</a></li>
+ <li><a href="/documentation/hadoop/index.html">Elephas - tools for RDF on Hadoop</a></li>
+ <li><a href="/documentation/query/text-query.html">Text Search</a></li>
+ <li><a href="/documentation/tdb/index.html">TDB</a></li>
+ <li><a href="/documentation/sdb/index.html">SDB</a></li>
+ <li><a href="/documentation/jdbc/index.html">SPARQL over JDBC</a></li>
+ <li><a href="/documentation/fuseki2/index.html">Fuseki</a></li>
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+ <li><a href="/documentation/tools/index.html">Command-line tools</a></li>
+ <li><a href="/documentation/extras/index.html">Extras</a></li>
+ </ul>
+ </li>
+
+ <li class="drop down">
+ <a href="#" class="dropdown-toggle" data-toggle="dropdown"><span class="glyphicon glyphicon-book"></span> Javadoc <b class="caret"></b></a>
+ <ul class="dropdown-menu">
+ <li><a href="/documentation/javadoc/jena/">Jena Core</a></li>
+ <li><a href="/documentation/javadoc/arq/">ARQ</a></li>
+ <li><a href="/documentation/javadoc/tdb/">TDB</a></li>
+ <li><a href="/documentation/javadoc/elephas/">Elephas</a></li>
+ <li><a href="/documentation/javadoc/text/">Text Search</a></li>
+ <li><a href="/documentation/javadoc/spatial/">Spatial Search</a></li>
+ <li><a href="/documentation/javadoc/permissions/">Permissions</a></li>
+ <li><a href="/documentation/javadoc/jdbc/">JDBC</a></li>
+ <li><a href="/documentation/javadoc/">All Javadoc</a></li>
+ </ul>
+ </li>
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+ <li id="ask"><a href="/help_and_support/index.html"><span class="glyphicon glyphicon-question-sign"></span> Ask</a></li>
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+ <li><a href="/about_jena/team.html">Project team</a></li>
+ <li><a href="/about_jena/contributions.html">Related projects</a></li>
+ <li class="divider"></li>
+ <li class="dropdown-header">ASF</li>
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+ <li><a href="http://www.apache.org/foundation/sponsorship.html">Become a Sponsor</a></li>
+ <li><a href="http://www.apache.org/security/">Security</a></li>
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+ <li id="edit"><a href="javascript:improveThisPage(location.href);" title="Improve this Page (Use username anonymous and empty password)"><span class="glyphicon glyphicon-pencil"></span> Improve this Page</a></li>
+ </ul>
+ </div>
+</div>
+</nav>
+
+
+<div class="container">
+ <div class="row">
+ <div class="col-md-12">
+ <div id="breadcrumbs"></div>
+ <h1 class="title">Apache Jena Initialization</h1>
+ <style type="text/css">
+/* The following code is added by mdx_elementid.py
+ It was originally lifted from http://subversion.apache.org/style/site.css */
+/*
+ * Hide class="elementid-permalink", except when an enclosing heading
+ * has the :hover property.
+ */
+.headerlink, .elementid-permalink {
+ visibility: hidden;
+}
+h2:hover > .headerlink, h3:hover > .headerlink, h1:hover > .headerlink, h6:hover > .headerlink, h4:hover > .headerlink, h5:hover > .headerlink, dt:hover > .elementid-permalink { visibility: visible }</style>
+<p>Jena has a simple initialization sequence that is
+used to setup components available at runtime.</p>
+<p>Application code is welcome to also use this mechanism. This
+must be done with care. Java initialization can lead to
+visibility of uninitialized data.</p>
+<p>The standard initialization sequence is<br/>
+Core -> RIOT -> ARQ -> TDB -> other (SDB, jena text, jena spatial)</p>
+<p>The sequence from core to TDB should be executed before application
+compoents. See below for how to control the order.</p>
+<p>Initialization occurs when <code>JenaSystem.init()</code> is first called. Jena ensures that this
+is done when the application first uses any Jena code by using class initializers.</p>
+<h2 id="initialization-code">Initialization code<a class="headerlink" href="#initialization-code" title="Permanent link">¶</a></h2>
+<p>Initialzation code is an implementation of <code>JenaSubsystemLifecycle</code>.
+and must have a zero-argument constructor.</p>
+<p><code>public interface JenaSubsystemLifecycle {
+ public void start() ;
+ public void stop() ;
+ default public int level() { return 9999 ; }
+}</code></p>
+<p>The code also supply a level, indicating its place in the order of initialization.
+The levels used by Jena are:</p>
+<ul>
+<li>0 - reserved</li>
+<li>10 - Used by jena-core</li>
+<li>20 - RIOT</li>
+<li>30 - ARQ</li>
+<li>40 - TDB</li>
+<li>9999 - other</li>
+</ul>
+<h2 id="the-initialization-process">The Initialization Process<a class="headerlink" href="#the-initialization-process" title="Permanent link">¶</a></h2>
+<p>The process followed by <code>JenaSystem.init()</code> is to obtain an instance of
+<code>JenaSubsystemRegistry</code>, ask it to <code>load()</code> initialization code, then call
+that code in an order based on declared level. The order of invocation
+of different initialization code within the same level is undefined
+and may be different from run to run.</p>
+<p>Only the first call of <code>JenaSystem.init()</code> causes the process to run.
+Any subsequent calls are cheap, so calling <code>JenaSystem.init()</code>
+when in doubt about the initialization state is safe.</p>
+<p>Overlapping concurrent calls to <code>JenaSystem.init()</code> are thread-safe.
+On a return from <code>JenaSystem.init()</code>, Jena has been initialized at some point.</p>
+<p>== The Standard Subsystem Registry</p>
+<p>The <code>JenaSubsystemRegistry</code> normally used is based on <code>java.util.ServiceLoader</code>.
+It looks for class resources
+<code>META-INF/services/org.apache.jena.system.JenaSubsystemLifecycle</code>
+on the classpath during the load step.</p>
+<p>See the javadoc for <code>java.util.ServiceLoader</code> for more details.</p>
+<p>See also the javadoc for
+<a href="/documentation/javadoc/jena/org/apache/jena/system/JenaSystem.html">JenaSystem</a>
+and the source code.</p>
+<h2 id="debugging">Debugging<a class="headerlink" href="#debugging" title="Permanent link">¶</a></h2>
+<p>There is a flag <code>JenaSystem.DEBUG_INIT</code> to help with development. It is not
+intended for runtime logging.</p>
+<p>Jena components print their initialization beginning and end points on
+<code>System.err</code> to help track down ordering issues.</p>
+<h2 id="modifying-the-standard-process">Modifying the Standard Process<a class="headerlink" href="#modifying-the-standard-process" title="Permanent link">¶</a></h2>
+<p>It is possible, with care, to alter the way
+that initialization code is discovered.</p>
+<p>An application can change the <code>JenaSubsystemRegistry</code> instance.
+This must be done before any Jena code is called anywhere
+in the current JVM. </p>
+<p>```
+ // Example alternative registry.
+ JenaSubsystemRegistry r = new JenaSubsystemRegistryBasic() {
+ @Override
+ public void load() {
+ if ( JenaSystem.DEBUG_INIT )
+ System.err.println("Example custom load") ;
+ super.load();
+ }
+ } ;</p>
+<div class="codehilite"><pre><span class="c1">// Set the sub-system registry</span>
+<span class="n">JenaSystem</span><span class="p">.</span><span class="n">setSubsystemRegistry</span><span class="p">(</span><span class="n">r</span><span class="p">);</span>
+
+<span class="c1">// Enable output if required</span>
+<span class="c1">// JenaSystem.DEBUG_INIT = true ;</span>
+
+<span class="c1">// Initialize Jena</span>
+<span class="n">JenaSystem</span><span class="p">.</span><span class="n">init</span><span class="p">()</span> <span class="p">;</span>
+</pre></div>
+
+
+<p>```</p>
+ </div>
+</div>
+
+</div><!--/.container -->
+
+ <footer class="footer">
+ <div class="container">
+ <p>Copyright © 2011–2015 The Apache Software Foundation, Licensed under
+ the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.
+ </p>
+ <p>
+ Apache Jena, Jena, the Apache Jena project logo,
+ Apache and the Apache feather logos are trademarks of The Apache Software Foundation.
+ </p>
+ </div>
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