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<!--
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<html>
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<head>
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<meta http-equiv="Content-Language" content="en-us">
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<link rel="stylesheet" type="text/css" href="../stylesheets/style.css">
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<title>PreSetDef Task</title>
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</head>
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<body>
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<h2 id="presetdef">PreSetDef</h2>
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<p><em>Since Apache Ant 1.6</em></p>
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<h3>Description</h3>
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<p>The preset definition generates a new definition based on a current definition with some
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attributes or elements preset.</p>
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<p>The resolution of properties in any of the attributes or nested text takes place with the
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definition is used and <em>not</em> when the preset definition is defined.</p>
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<h3>Parameters</h3>
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<table class="attr">
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<tr>
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<th scope="col">Attribute</th>
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<th scope="col">Description</th>
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<th scope="col">Required</th>
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</tr>
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<tr>
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<td>name</td>
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<td>the name of the new definition</td>
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<td>Yes</td>
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</tr>
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<tr>
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<td>uri</td>
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<td>The URI that this definition should live in.</td>
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<td>No</td>
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</tr>
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</table>
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<h3>Parameters specified as nested elements</h3>
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<h4>another type with attributes or elements set</h4>
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<p>The <code><presetdef></code> task takes one nested element as a parameter. This nested
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element can be any other type or task. The attributes and elements that need to be preset are
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placed here.</p>
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<h3>Examples</h3>
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<p>The following fragment defines a <code>javac</code> task with
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the <var>debug</var>, <var>deprecation</var>, <var>srcdir</var> and <var>destdir</var>
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attributes set. It also has a <code>src</code> element to source files from a generated
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directory.</p>
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<pre>
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<presetdef name="my.javac">
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<javac debug="${debug}" deprecation="${deprecation}"
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srcdir="${src.dir}" destdir="${classes.dir}">
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<src path="${gen.dir}"/>
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</javac>
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</presetdef></pre>
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<p>This can be used as a normal <code>javac</code> task—for example:</p>
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<pre><my.javac/></pre>
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<p>The attributes specified in the preset task may be overridden—i.e. they may be seen as
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optional attributes—for example:</p>
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<pre><my.javac srcdir="${test.src}" deprecation="no"/></pre>
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<p>One may put a <code>presetdef</code> definition in an antlib. For example suppose the jar
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file <samp>antgoodies.jar</samp> has the <samp>antlib.xml</samp> as follows:</p>
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<pre>
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<antlib>
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<taskdef resource="com/acme/antgoodies/tasks.properties"/>
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<!-- Implement the common use of the javac command -->
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<presetdef name="javac">
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<javac deprecation="${deprecation}" debug="${debug}"
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srcdir="src" destdir="classes"/>
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</presetdef>
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</antlib></pre>
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<p>One may then use this in a build file as follows:</p>
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<pre>
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<project default="example" xmlns:antgoodies="antlib:com.acme.antgoodies">
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<target name="example">
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<!-- Compile source -->
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<antgoodies:javac srcdir="src/main"/>
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<!-- Compile test code -->
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<antgoodies:javac srcdir="src/test"/>
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</target>
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</project></pre>
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<p>The following is an example of evaluation of properties when the definition is used:</p>
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<pre>
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<target name="defineandcall">
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<presetdef name="showmessage">
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<echo>message is '${message}'</echo>
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</presetdef>
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<showmessage/>
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<property name="message" value="Message 1"/>
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<showmessage/>
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<antcall target="called">
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<param name="message" value="Message 2"/>
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</antcall>
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</target>
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<target name="called">
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<showmessage/>
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</target></pre>
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<p>The command <kbd>ant defineandcall</kbd> results in the output:</p>
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<pre class="output">
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defineandcall:
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[showmessage] message is '${message}'
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[showmessage] message is 'Message 1'
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called:
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[showmessage] message is 'Message 2'</pre>
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<p>It is possible to use a trick to evaluate properties when the definition is <em>made</em>
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rather than used. This can be useful if you do not expect some properties to be available in
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child builds run with <code><ant ... inheritall="false"></code>:</p>
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<pre>
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<macrodef name="showmessage-presetdef">
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<attribute name="messageval"/>
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<presetdef name="showmessage">
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<echo>message is '@{messageval}'</echo>
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</presetdef>
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</macrodef>
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<showmessage-presetdef messageval="${message}"/></pre>
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</body>
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</html>
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