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<title>PreSetDef Task</title>
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<h2 id="presetdef">PreSetDef</h2>
<p><em>Since Apache Ant 1.6</em></p>
<h3>Description</h3>
<p>The preset definition generates a new definition based on a current definition with some
attributes or elements preset.</p>
<p>The resolution of properties in any of the attributes or nested text takes place with the
definition is used and <em>not</em> when the preset definition is defined.</p>
<h3>Parameters</h3>
<table class="attr">
<tr>
<th scope="col">Attribute</th>
<th scope="col">Description</th>
<th scope="col">Required</th>
</tr>
<tr>
<td>name</td>
<td>the name of the new definition</td>
<td>Yes</td>
</tr>
<tr>
<td>uri</td>
<td>The URI that this definition should live in.</td>
<td>No</td>
</tr>
</table>
<h3>Parameters specified as nested elements</h3>
<h4>another type with attributes or elements set</h4>
<p>The <code><presetdef></code> task takes one nested element as a parameter. This nested
element can be any other type or task. The attributes and elements that need to be preset are
placed here.</p>
<h3>Examples</h3>
<p>The following fragment defines a <code>javac</code> task with
the <var>debug</var>, <var>deprecation</var>, <var>srcdir</var> and <var>destdir</var>
attributes set. It also has a <code>src</code> element to source files from a generated
directory.</p>
<pre>
<presetdef name="my.javac">
<javac debug="${debug}" deprecation="${deprecation}"
srcdir="${src.dir}" destdir="${classes.dir}">
<src path="${gen.dir}"/>
</javac>
</presetdef></pre>
<p>This can be used as a normal <code>javac</code> task—for example:</p>
<pre><my.javac/></pre>
<p>The attributes specified in the preset task may be overridden—i.e. they may be seen as
optional attributes—for example:</p>
<pre><my.javac srcdir="${test.src}" deprecation="no"/></pre>
<p>One may put a <code>presetdef</code> definition in an antlib. For example suppose the jar
file <samp>antgoodies.jar</samp> has the <samp>antlib.xml</samp> as follows:</p>
<pre>
<antlib>
<taskdef resource="com/acme/antgoodies/tasks.properties"/>
<!-- Implement the common use of the javac command -->
<presetdef name="javac">
<javac deprecation="${deprecation}" debug="${debug}"
srcdir="src" destdir="classes"/>
</presetdef>
</antlib></pre>
<p>One may then use this in a build file as follows:</p>
<pre>
<project default="example" xmlns:antgoodies="antlib:com.acme.antgoodies">
<target name="example">
<!-- Compile source -->
<antgoodies:javac srcdir="src/main"/>
<!-- Compile test code -->
<antgoodies:javac srcdir="src/test"/>
</target>
</project></pre>
<p>The following is an example of evaluation of properties when the definition is used:</p>
<pre>
<target name="defineandcall">
<presetdef name="showmessage">
<echo>message is '${message}'</echo>
</presetdef>
<showmessage/>
<property name="message" value="Message 1"/>
<showmessage/>
<antcall target="called">
<param name="message" value="Message 2"/>
</antcall>
</target>
<target name="called">
<showmessage/>
</target></pre>
<p>The command <kbd>ant defineandcall</kbd> results in the output:</p>
<pre class="output">
defineandcall:
[showmessage] message is '${message}'
[showmessage] message is 'Message 1'
called:
[showmessage] message is 'Message 2'</pre>
<p>It is possible to use a trick to evaluate properties when the definition is <em>made</em>
rather than used. This can be useful if you do not expect some properties to be available in
child builds run with <code><ant ... inheritall="false"></code>:</p>
<pre>
<macrodef name="showmessage-presetdef">
<attribute name="messageval"/>
<presetdef name="showmessage">
<echo>message is '@{messageval}'</echo>
</presetdef>
</macrodef>
<showmessage-presetdef messageval="${message}"/></pre>
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