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<title>The Command Line Processor Plugin: ArgumentProcessor</title>
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<h1>The Command Line Processor Plugin: ArgumentProcessor</h1>

<h2 id="definition">What is an ArgumentProcessor?</h2>

<p>
An <code class="code">ArgumentProcessor</code> is a parser of command line argument which is then
call before and after the build file is being parsed. Third party libraries may then be able to have
custom argument line argument which modify Ant behaviour.
</p>

<p>
An <code class="code">ArgumentProcessor</code> is called each time Ant parse an unknown argument,
an <code class="code">ArgumentProcessor</code> doesn't take precedence over Ant to parse already
supported options. It is then recommended to third party <code class="code">ArgumentProcessor</code>
implementation to chose specific 'enough' argument name, avoiding for instance one letter arguments.
</p>

<p>
It is also called at the different phases so different behaviour can be implemented. It is called
just after every arguments are parsed, just before the project is being configured (the build file
being parsed), and just after. Some of the methods to be implemented return a boolean:
if <q>true</q> is returned, Ant will terminate immediately, without error.
</p>

<p>
Being called during all these phases, an <code class="code">ArgumentProcessor</code> can just print
some specific system properties and quit (like <kbd>-diagnose</kbd>), or print some specific
properties of a project after being parsed and quit (like <kbd>-projectHelp</kbd>), or just set some
custom properties on the project and let it run.
</p>

<h2 id="repository">How to register it's own ArgumentProcessor</h2>

<p>First, the <code class="code">ArgumentProcessor</code> must be an implementation
of <code class="code">org.apache.tools.ant.ArgumentProcessor</code>.
</p>

<p>Then to declare it: create a
file <samp>META-INF/services/org.apache.tools.ant.ArgumentProcessor</samp> which contains only one
line the fully qualified name of the class of the implementation. This file together with the
implementation class need then to be found in Ant's classpath.
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