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<title>How Plugins are Loaded</title><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="index.html" title="jEdit 5.6 User's Guide"><link rel="up" href="plugin-implement.html" title="Chapter 18. Implementing a Simple Plugin"><link rel="prev" href="plugin-implement.html" title="Chapter 18. Implementing a Simple Plugin"><link rel="next" href="plugin-implement-quicknotepadplugin.html" title="The QuickNotepadPlugin Class"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"> How Plugins are Loaded</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="plugin-implement.html">Prev</a> </td><th width="60%" align="center">Chapter 18. Implementing a Simple Plugin</th><td width="20%" align="right"> <a accesskey="n" href="plugin-implement-quicknotepadplugin.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="plugin-load"></a><a class="indexterm" name="d0e13961"></a> How Plugins are Loaded</h2></div></div></div><p>We will discuss the implementation of the
<span class="application">QuickNotepad</span> plugin, along with the jEdit
APIs it makes use of. But first, we describe how plugins are
loaded.</p><p>As part of its startup routine, jEdit's main
method calls various methods to load and initialize plugins.</p><p>Additionally, plugins using the jEdit 4.2 plugin API can be loaded
and unloaded at any time. This is a great help when developing your own
plugins -- there is no need to restart the editor after making changes
(see <a class="xref" href="plugin-implement-reloading.html" title="Reloading the Plugin">the section called “Reloading the Plugin”</a> ).</p><p>Plugins are loaded from files with the <code class="filename">.jar</code>
filename extension located in the <code class="filename">jars</code>
subdirectories of the jEdit installation and user settings directories
(see <a class="xref" href="settings-directory.html" title="The jEdit Settings Directory">the section called “The jEdit Settings Directory”</a>).</p><p>For each JAR archive file it finds, jEdit scans its entries and
performs the following tasks:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>Adds to a collection maintained by jEdit a new object of
type <a class="ulink" href="../api/org/gjt/sp/jedit/PluginJAR.html" target="_top">
<code class="classname">PluginJAR</code></a>. This is a data
structure holding the name of the JAR archive file, a reference
to the <a class="ulink" href="../api/org/gjt/sp/jedit/JARClassLoader.html" target="_top">
<code class="classname">JARClassLoader</code></a>, and a collection
of plugins found in the archive file.</p></li><li class="listitem"><p>Loads any properties defined in files ending with the
extension <code class="filename">.props</code> that are contained in the
archive. See <a class="xref" href="plugin-implement-properties.html" title="The Property Files">the section called “The Property Files”</a>.</p></li><li class="listitem"><p>Reads action definitions from any file named
<code class="filename">actions.xml</code> in the archive (the file need
not be at the top level). See <a class="xref" href="plugin-implement-actions.html" title="The Actions.xml Catalog">the section called “The Actions.xml Catalog”</a>.</p></li><li class="listitem"><p>Parses and loads the contents of any file named
<code class="filename">dockables.xml</code> in the archive (the file need
not be at the top level). This file contains BeanShell code for
creating docking or floating windows that will contain the
visible components of the plugin. Not all plugins define
dockable windows, but those that do need a
<code class="filename">dockables.xml</code> file. See <a class="xref" href="plugin-implement-dockables.html" title="The dockables.xml Window Catalog">the section called “The dockables.xml Window Catalog”</a>.</p></li><li class="listitem"><p>Checks for a class name with a name ending with
<code class="filename">Plugin.class</code>.</p><p>Such a class is known as a <em class="firstterm">plugin core
class</em> and must extend jEdit's abstract
<code class="classname">EditPlugin</code></a> class.</p><p>The initialization routine checks the plugin's properties
to see if it is subject to any dependencies. For example, a
plugin may require that the version of the Java runtime
environment or of jEdit itself be equal to or above some
threshold version. A plugin can also require the presence of
another plugin.</p><p>If any dependency is not satisfied, the loader marks the
plugin as <span class="quote">“<span class="quote">broken</span>”</span> and logs an error
message.</p></li></ul></div><p>After scanning the plugin JAR file and loading any resources, a
new instance of the plugin core class is created and added to the
collection maintained by the appropriate <a class="ulink" href="../api/org/gjt/sp/jedit/PluginJAR.html" target="_top">
<code class="classname">PluginJAR</code></a>. jEdit then calls the
<code class="function">start()</code> method of the plugin core class. The
<code class="function">start()</code> method can perform initialization of the
object's data members. Because this method is defined as an empty
<span class="quote">“<span class="quote">no-op</span>”</span> in the <a class="ulink" href="../api/org/gjt/sp/jedit/EditPlugin.html" target="_top">
<code class="classname">EditPlugin</code></a> abstract class, a plugin need
not provide an implementation if no unique initialization is
required.</p></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plugin-implement.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plugin-implement.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plugin-implement-quicknotepadplugin.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 18. Implementing a Simple Plugin </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> The QuickNotepadPlugin Class</td></tr></table></div></body></html>
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