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352 lines
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HTML
352 lines
13 KiB
HTML
<!DOCTYPE html>
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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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The ASF licenses this file to You under the Apache License, Version 2.0
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<html lang="en">
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<head>
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<link rel="stylesheet" type="text/css" href="../stylesheets/style.css">
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<title>Custom Components</title>
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</head>
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<body>
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<h2>Custom Components</h2>
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<h3>Overview</h3>
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<p>
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Custom components are conditions, selectors, filters and other objects that are defined
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outside Apache Ant core.
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</p>
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<p>
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In Ant 1.6 custom conditions, selectors and filters has been overhauled.
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</p>
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<p>
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It is now possible to define custom conditions, selectors and filters that behave like Ant
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Core components. This is achieved by allowing datatypes defined in build scripts to be used
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as custom components if the class of the datatype is compatible, or has been adapted by an
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adapter class.
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</p>
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<p>
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The old methods of defining custom components are still supported.
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</p>
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<h3>Definition and Use</h3>
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<p>
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A custom component is a normal Java class that implements a particular interface or extends a
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particular class, or has been adapted to the interface or class.
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</p>
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<p>
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It is exactly like writing a <a href="../develop.html#writingowntask">custom task</a>. One
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defines attributes and nested elements by writing <em>setter</em> methods and <em>add</em>
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methods.
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</p>
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<p>
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After the class has been written, it is added to the ant system by
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using <code><typedef></code>.
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</p>
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<h3 id="customconditions">Custom Conditions</h3>
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<p>
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Custom conditions are datatypes that
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implement <code class="code">org.apache.tools.ant.taskdefs.condition.Condition</code>. For
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example a custom condition that returns true if a string is all upper case could be written
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as:
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</p>
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<pre>
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package com.mydomain;
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import org.apache.tools.ant.BuildException;
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import org.apache.tools.ant.taskdefs.condition.Condition;
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public class AllUpperCaseCondition implements Condition {
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private String value;
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// The setter for the "value" attribute
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public void setValue(String value) {
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this.value = value;
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}
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// This method evaluates the condition
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public boolean eval() {
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if (value == null) {
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throw new BuildException("value attribute is not set");
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}
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return value.toUpperCase().equals(value);
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}
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}</pre>
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<p>
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Adding the condition to the system is achieved as follows:
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</p>
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<pre>
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<typedef
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name="alluppercase"
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classname="com.mydomain.AllUpperCaseCondition"
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classpath="${mydomain.classes}"/></pre>
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<p>
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This condition can now be used wherever a Core Ant condition is used.
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</p>
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<pre>
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<condition property="allupper">
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<alluppercase value="THIS IS ALL UPPER CASE"/>
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</condition></pre>
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<h3 id="customselectors">Custom Selectors</h3>
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<p>
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Custom selectors are datatypes that
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implement <code class="code">org.apache.tools.ant.types.selectors.FileSelector</code>.
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</p>
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<p>
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There is only one method required, <code class="code">public boolean isSelected(File basedir,
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String filename, File file)</code>. It returns true or false depending on whether the given
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file should be selected or not.
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</p>
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<p>
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An example of a custom selection that selects filenames ending
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in <samp>.java</samp> would be:
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</p>
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<pre>
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package com.mydomain;
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import java.io.File;
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import org.apache.tools.ant.types.selectors.FileSelector;
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public class JavaSelector implements FileSelector {
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public boolean isSelected(File b, String filename, File f) {
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return filename.toLowerCase().endsWith(".java");
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}
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}</pre>
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<p>
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Adding the selector to the system is achieved as follows:
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</p>
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<pre>
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<typedef
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name="javaselector"
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classname="com.mydomain.JavaSelector"
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classpath="${mydomain.classes}"/></pre>
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<p>
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This selector can now be used wherever a Core Ant selector is used, for example:
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</p>
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<pre>
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<copy todir="to">
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<fileset dir="src">
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<javaselector/>
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</fileset>
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</copy></pre>
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<p>
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One may use <code class="code">org.apache.tools.ant.types.selectors.BaseSelector</code>, a
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convenience class that provides reasonable default behaviour. It has some predefined
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behaviours you can take advantage of. Any time you encounter a problem when setting attributes
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or adding tags, you can call <code class="code">setError(String errmsg)</code> and the class
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will know that there is a problem. Then, at the top of
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your <code class="code">isSelected()</code> method call <code class="code">validate()</code>
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and a <code>BuildException</code> will be thrown with the contents of your error
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message. The <code class="code">validate()</code> method also gives you a last chance to check
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your settings for consistency because it
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calls <code class="code">verifySettings()</code>. Override this method and
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call <code class="code">setError()</code> within it if you detect any problems in how your
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selector is set up.
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</p>
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<p>
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To write custom selector containers one should
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extend <code class="code">org.apache.tools.ant.types.selectors.BaseSelectorContainer</code>.
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Implement the <code class="code">public boolean isSelected(File baseDir, String filename, File
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file)</code> method to do the right thing. Chances are you'll want to iterate over the
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selectors under you, so use <code class="code">selectorElements()</code> to get an iterator
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that will do that.
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</p>
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<p>
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For example to create a selector container that will select files if a certain number of
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contained selectors select, one could write a selector as follows:
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</p>
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<pre>
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public class MatchNumberSelectors extends BaseSelectorContainer {
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private int number = -1;
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public void setNumber(int number) {
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this.number = number;
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}
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public void verifySettings() {
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if (number < 0) {
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throw new BuildException("Number attribute should be set");
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}
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}
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public boolean isSelected(File baseDir, String filename, File file) {
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validate();
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int numberSelected = 0;
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for (Enumeration e = selectorElements(); e.hasNextElement();) {
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FileSelector s = (FileSelector) e.nextElement();
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if (s.isSelected(baseDir, filename, file)) {
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numberSelected++;
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}
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}
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return numberSelected == number;
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}
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}</pre>
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<p>
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To define and use this selector one could do:
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</p>
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<pre>
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<typedef name="numberselected"
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classname="com.mydomain.MatchNumberSelectors"/>
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...
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<fileset dir="${src.path}">
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<numberselected number="2">
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<contains text="script" casesensitive="no"/>
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<size value="4" units="Ki" when="more"/>
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<javaselector/>
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</numberselected>
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</fileset></pre>
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<p>
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<em>The custom selector</em>
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</p>
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<p>
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The custom selector was the pre Ant 1.6 way of defining custom selectors. This method is
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still supported for backward compatibility.
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</p>
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<p>
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You can write your own selectors and use them within the selector containers by specifying
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them within the <code><custom></code> tag.
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</p>
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<p>
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To create a new Custom Selector, you have to create a class that
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implements <code class="code">org.apache.tools.ant.types.selectors.ExtendFileSelector</code>.
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The easiest way to do that is through the convenience base
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class <code class="code">org.apache.tools.ant.types.selectors.BaseExtendSelector</code>, which
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provides all of the methods for supporting <code><param></code> tags. First, override
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the <code class="code">isSelected()</code> method, and optionally
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the <code class="code">verifySettings()</code> method. If your custom selector requires
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parameters to be set, you can also override the <code class="code">setParameters()</code>
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method and interpret the parameters that are passed in any way you like. Several of the core
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selectors demonstrate how to do that because they can also be used as custom selectors.
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</p>
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<p>
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Once that is written, you include it in your build file by using
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the <code><custom></code> tag.
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</p>
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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>classname</td>
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<td>
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The name of your class that
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implements <code class="code">org.apache.tools.ant.types.selectors.FileSelector</code>.
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</td>
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<td>Yes</td>
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</tr>
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<tr>
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<td>classpath</td>
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<td>
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The classpath to use in order to load the custom selector class. If
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neither <var>classpath</var> nor <var>classpathref</var> are specified, the class will be
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loaded from the classpath that Ant uses.
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</td>
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<td>No</td>
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</tr>
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<tr>
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<td>classpathref</td>
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<td>
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A reference to a classpath previously defined. If neither <var>classpathref</var>
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nor <var>classpath</var> above are specified, the class will be loaded from the classpath
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that Ant uses.
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</td>
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<td>No</td>
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</tr>
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</table>
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<p>
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Here is how you use <code><custom></code> to use your class as a selector:
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</p>
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<pre>
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<fileset dir="${mydir}" includes="**/*">
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<custom classname="com.mydomain.MySelector">
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<param name="myattribute" value="myvalue"/>
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</custom>
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</fileset></pre>
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<p>The core selectors that can also be used as custom selectors are</p>
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<ul>
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<li><a href="selectors.html#containsselect">Contains Selector</a> with
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classname <code class="code">org.apache.tools.ant.types.selectors.ContainsSelector</code></li>
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<li><a href="selectors.html#dateselect">Date Selector</a> with
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classname <code class="code">org.apache.tools.ant.types.selectors.DateSelector</code></li>
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<li><a href="selectors.html#depthselect">Depth Selector</a> with
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classname <code class="code">org.apache.tools.ant.types.selectors.DepthSelector</code></li>
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<li><a href="selectors.html#filenameselect">Filename Selector</a> with
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classname <code class="code">org.apache.tools.ant.types.selectors.FilenameSelector</code></li>
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<li><a href="selectors.html#sizeselect">Size Selector</a> with
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classname <code class="code">org.apache.tools.ant.types.selectors.SizeSelector</code></li>
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</ul>
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<p>
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Here is the example from the Depth Selector section rewritten to use the selector
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through <code><custom></code>.
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</p>
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<pre>
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<fileset dir="${doc.path}" includes="**/*">
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<custom classname="org.apache.tools.ant.types.selectors.DepthSelector">
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<param name="max" value="1"/>
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</custom>
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</fileset></pre>
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<p>Selects all files in the base directory and one directory below that.</p>
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<h3 id="filterreaders">Custom Filter Readers</h3>
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<p>
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Custom filter readers selectors are datatypes that
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implement <code class="code">org.apache.tools.ant.types.filters.ChainableReader</code>.
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</p>
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<p>
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There is only one method required, <code class="code">Reader chain(Reader reader)</code>.
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This returns a reader that filters input from the specified reader.
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</p>
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<p>
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For example a filterreader that removes every second character could be:
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</p>
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<pre>
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public class RemoveOddCharacters implements ChainableReader {
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public Reader chain(Reader reader) {
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return new BaseFilterReader(reader) {
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int count = 0;
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public int read() throws IOException {
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while (true) {
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int c = in.read();
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if (c == -1) {
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return c;
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}
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count++;
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if ((count % 2) == 1) {
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return c;
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}
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}
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}
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}
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}
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}</pre>
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<p>
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For line oriented filters it may be easier to
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extend <code class="code">ChainableFilterReader</code> an inner class
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of <code class="code">org.apache.tools.ant.filters.TokenFilter</code>.
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</p>
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<p>
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For example a filter that appends the line number could be
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</p>
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<pre>
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public class AddLineNumber extends ChainableReaderFilter {
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private void lineNumber = 0;
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public String filter(String string) {
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lineNumber++;
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return "" + lineNumber + "\t" + string;
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}
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}</pre>
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</body>
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</html>
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