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| 2 | <head>
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| 3 | <meta http-equiv="Content-Language" content="en-us"></meta>
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| 4 | <title>Custom Components</title>
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| 5 | <link rel="stylesheet" type="text/css" href="../stylesheets/antmanual.css">
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| 6 | </head>
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| 7 | <body>
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| 8 | <h2>Custom Components</h2>
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| 9 | <h3>Overview</h3>
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| 10 | <p>
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| 11 | Custom components are conditions, selectors, filters and other
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| 12 | objects that are defined outside ant core.
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| 13 | </p>
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| 14 | <p>
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| 15 | In Ant 1.6 custom conditions, selectors and filters has
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| 16 | been overhauled.
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| 17 | </p>
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| 18 | <p>
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| 19 | It is now possible to define custom conditions, selectors and filters
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| 20 | that behave like Ant Core components.
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| 21 | This is achieved by allowing datatypes defined in build scripts
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| 22 | to be used as custom components if the class of the datatype
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| 23 | is compatible, or has been adapted by an adapter class.
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| 24 | </p>
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| 25 | <p>
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| 26 | The old methods of defining custom components are still supported.
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| 27 | </p>
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| 28 | <h3>Definition and use</h3>
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| 29 | <p>
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| 30 | A custom component is a normal Java class that implements a particular
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| 31 | interface or extends a particular class, or has been adapted to the
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| 32 | interface or class.
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| 33 | </p>
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| 34 | <p>
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| 35 | It is exactly like writing a
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| 36 | <a href="../develop.html#writingowntask">custom task</a>.
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| 37 | One defines attributes and nested elements by writing <i>setter</i>
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| 38 | methods and <i>add</i> methods.
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| 39 | </p>
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| 40 | <p>
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| 41 | After the class has been written, it is added to the ant system
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| 42 | by using <code><typedef></code>.
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| 43 | </p>
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| 44 | <h3><a name="customconditions">Custom Conditions</a></h3>
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| 45 | <p>
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| 46 | Custom conditions are datatypes that implement
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| 47 | <code>org.apache.tools.ant.taskdefs.condition.Condition</code>.
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| 48 | For example a custom condition that returns true if a
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| 49 | string is all upper case could be written as:
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| 50 | </p>
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| 51 | <blockquote>
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| 52 | <pre>
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| 53 | package com.mydomain;
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| 54 |
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| 55 | import org.apache.tools.ant.BuildException;
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| 56 | import org.apache.tools.ant.taskdefs.condition.Condition;
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| 57 |
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| 58 | public class AllUpperCaseCondition implements Condition {
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| 59 | private String value;
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| 60 |
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| 61 | // The setter for the "value" attribute
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| 62 | public void setValue(String value) {
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| 63 | this.value = value;
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| 64 | }
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| 65 |
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| 66 | // This method evaluates the condition
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| 67 | public boolean eval() {
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| 68 | if (value == null) {
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| 69 | throw new BuildException("value attribute is not set");
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| 70 | }
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| 71 | return value.toUpperCase().equals(value);
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| 72 | }
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| 73 | }
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| 74 | </pre>
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| 75 | </blockquote>
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| 76 |
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| 77 | <p>
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| 78 | Adding the condition to the system is achieved as follows:
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| 79 | </p>
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| 80 | <blockquote>
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| 81 | <pre>
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| 82 | <typedef
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| 83 | name="alluppercase"
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| 84 | classname="com.mydomain.AllUpperCaseCondition"
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| 85 | classpath="${mydomain.classes}"/>
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| 86 | </pre>
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| 87 | </blockquote>
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| 88 | <p>
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| 89 | This condition can now be used wherever a Core Ant condition
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| 90 | is used.
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| 91 | </p>
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| 92 | <blockquote>
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| 93 | <pre>
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| 94 | <condition property="allupper">
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| 95 | <alluppercase value="THIS IS ALL UPPER CASE"/>
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| 96 | </condition>
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| 97 | </pre>
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| 98 | </blockquote>
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| 99 | <h3><a name="customselectors">Custom Selectors</a></h3>
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| 100 | <p>
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| 101 | Custom selectors are datatypes that implement
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| 102 | <code>org.apache.tools.ant.types.selectors.FileSelector</code>.
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| 103 | </p>
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| 104 | <p>There is only one method required.
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| 105 | <code>public boolean isSelected(File basedir, String filename,
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| 106 | File file)</code>.
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| 107 | It returns true
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| 108 | or false depending on whether the given file should be
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| 109 | selected or not.
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| 110 | </p>
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| 111 | <p>
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| 112 | An example of a custom selection that selects filenames ending
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| 113 | in ".java" would be:
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| 114 | </p>
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| 115 | <blockquote>
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| 116 | <pre>
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| 117 | package com.mydomain;
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| 118 | import java.io.File;
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| 119 | import org.apache.tools.ant.types.selectors.FileSelector;
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| 120 | public class JavaSelector implements FileSelector {
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| 121 | public boolean isSelected(File b, String filename, File f) {
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| 122 | return filename.toLowerCase().endsWith(".java");
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| 123 | }
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| 124 | }
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| 125 | </pre>
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| 126 | </blockquote>
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| 127 | <p>
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| 128 | Adding the selector to the system is achieved as follows:
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| 129 | </p>
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| 130 | <blockquote>
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| 131 | <pre>
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| 132 | <typedef
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| 133 | name="javaselector"
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| 134 | classname="com.mydomain.JavaSelector"
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| 135 | classpath="${mydomain.classes}"/>
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| 136 | </pre>
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| 137 | </blockquote>
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| 138 | <p>
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| 139 | This selector can now be used wherever a Core Ant selector
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| 140 | is used, for example:
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| 141 | </p>
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| 142 | <blockquote>
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| 143 | <pre>
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| 144 | <copy todir="to">
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| 145 | <fileset dir="src">
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| 146 | <javaselector/>
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| 147 | </fileset>
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| 148 | </copy>
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| 149 | </pre>
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| 150 | </blockquote>
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| 151 |
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| 152 | <p>
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| 153 | One may use
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| 154 | <code>org.apache.tools.ant.types.selectors.BaseSelector</code>,
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| 155 | a convenience class that provides reasonable default
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| 156 | behaviour.
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| 157 | It has some predefined behaviours you can take advantage
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| 158 | of. Any time you encounter a problem when setting attributes or
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| 159 | adding tags, you can call setError(String errmsg) and the class
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| 160 | will know that there is a problem. Then, at the top of your
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| 161 | <code>isSelected()</code> method call <code>validate()</code> and
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| 162 | a BuildException will be thrown with the contents of your error
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| 163 | message. The <code>validate()</code> method also gives you a
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| 164 | last chance to check your settings for consistency because it
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| 165 | calls <code>verifySettings()</code>. Override this method and
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| 166 | call <code>setError()</code> within it if you detect any
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| 167 | problems in how your selector is set up.
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| 168 | </p>
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| 169 | <p>
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| 170 | To write custom selector containers one should extend
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| 171 | <code>org.apache.tools.ant.types.selectors.BaseSelectorContainer</code>.
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| 172 | Implement the
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| 173 | <code>public boolean isSelected(File baseDir, String filename, File file)</code>
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| 174 | method to do the right thing. Chances are you'll want to iterate
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| 175 | over the selectors under you, so use
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| 176 | <code>selectorElements()</code> to get an iterator that will do
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| 177 | that.
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| 178 | </p>
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| 179 | <p>
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| 180 | For example to create a selector container that will select files
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| 181 | if a certain number of contained selectors select, one could write
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| 182 | a selector as follows:
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| 183 | </p>
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| 184 | <blockquote>
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| 185 | <pre>
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| 186 | public class MatchNumberSelectors extends BaseSelectorContainer {
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| 187 | private int number = -1;
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| 188 | public void setNumber(int number) {
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| 189 | this.number = number;
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| 190 | }
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| 191 | public void verifySettings() {
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| 192 | if (number < 0) {
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| 193 | throw new BuildException("Number attribute should be set");
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| 194 | }
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| 195 | }
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| 196 | public boolean isSelected(File baseDir, String filename, File file) {
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| 197 | validate();
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| 198 | int numberSelected = 0;
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| 199 | for (Enumeration e = selectorElements(); e.hasNextElement();) {
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| 200 | FileSelector s = (FileSelector) e.nextElement();
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| 201 | if (s.isSelected(baseDir, filename, file)) {
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| 202 | numberSelected++;
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| 203 | }
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| 204 | }
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| 205 | return numberSelected == number;
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| 206 | }
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| 207 | }
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| 208 | </pre>
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| 209 | </blockquote>
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| 210 | <p>
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| 211 | To define and use this selector one could do:
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| 212 | </p>
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| 213 | <blockquote>
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| 214 | <pre>
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| 215 | <typedef name="numberselected"
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| 216 | classname="com.mydomain.MatchNumberSelectors"/>
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| 217 | ...
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| 218 | <fileset dir="${src.path}">
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| 219 | <numberselected number="2">
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| 220 | <contains text="script" casesensitive="no"/>
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| 221 | <size value="4" units="Ki" when="more"/>
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| 222 | <javaselector/>
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| 223 | </numberselected>
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| 224 | </fileset>
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| 225 | </pre>
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| 226 | </blockquote>
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| 227 | <p>
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| 228 | <i>The custom selector</i>
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| 229 | </p>
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| 230 | <p>
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| 231 | The custom selector was the pre ant 1.6 way of defining custom selectors.
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| 232 | This method is still supported for backward compatibility.
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| 233 | </p>
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| 234 | <p>You can write your own selectors and use them within the selector
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| 235 | containers by specifying them within the <code><custom></code> tag.</p>
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| 236 |
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| 237 | <p>To create a new Custom Selector, you have to create a class that
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| 238 | implements
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| 239 | <code>org.apache.tools.ant.types.selectors.ExtendFileSelector</code>.
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| 240 | The easiest way to do that is through the convenience base class
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| 241 | <code>org.apache.tools.ant.types.selectors.BaseExtendSelector</code>,
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| 242 | which provides all of the methods for supporting
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| 243 | <code><param></code> tags. First, override the
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| 244 | <code>isSelected()</code> method, and optionally the
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| 245 | <code>verifySettings()</code> method. If your custom
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| 246 | selector requires parameters to be set, you can also override
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| 247 | the <code>setParameters()</code> method and interpret the
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| 248 | parameters that are passed in any way you like. Several of the
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| 249 | core selectors demonstrate how to do that because they can
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| 250 | also be used as custom selectors.</p>
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| 251 |
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| 252 |
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| 253 | <p>Once that is written, you include it in your build file by using
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| 254 | the <code><custom></code> tag.
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| 255 | </p>
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| 256 |
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| 257 | <table border="1" cellpadding="2" cellspacing="0">
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| 258 | <tr>
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| 259 | <td valign="top"><b>Attribute</b></td>
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| 260 | <td valign="top"><b>Description</b></td>
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| 261 | <td align="center" valign="top"><b>Required</b></td>
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| 262 | </tr>
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| 263 | <tr>
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| 264 | <td valign="top">classname</td>
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| 265 | <td valign="top">The name of your class that implements
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| 266 | <code>org.apache.tools.ant.types.selectors.FileSelector</code>.
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| 267 | </td>
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| 268 | <td valign="top" align="center">Yes</td>
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| 269 | </tr>
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| 270 | <tr>
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| 271 | <td valign="top">classpath</td>
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| 272 | <td valign="top">The classpath to use in order to load the
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| 273 | custom selector class. If neither this classpath nor the
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| 274 | classpathref are specified, the class will be
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| 275 | loaded from the classpath that Ant uses.
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| 276 | </td>
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| 277 | <td valign="top" align="center">No</td>
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| 278 | </tr>
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| 279 | <tr>
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| 280 | <td valign="top">classpathref</td>
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| 281 | <td valign="top">A reference to a classpath previously
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| 282 | defined. If neither this reference nor the
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| 283 | classpath above are specified, the class will be
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| 284 | loaded from the classpath that Ant uses.
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| 285 | </td>
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| 286 | <td valign="top" align="center">No</td>
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| 287 | </tr>
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| 288 | </table>
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| 289 |
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| 290 | <p>Here is how you use <code><custom></code> to
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| 291 | use your class as a selector:
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| 292 | </p>
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| 293 |
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| 294 | <blockquote><pre>
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| 295 | <fileset dir="${mydir}" includes="**/*">
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| 296 | <custom classname="com.mydomain.MySelector">
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| 297 | <param name="myattribute" value="myvalue"/>
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| 298 | </custom>
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| 299 | </fileset>
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| 300 | </pre></blockquote>
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| 301 |
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| 302 |
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| 303 | <p>The core selectors that can also be used as custom selectors
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| 304 | are</p>
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| 305 |
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| 306 | <ul>
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| 307 | <li><a href="selectors.html#containsselect">Contains Selector</a> with
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| 308 | classname <code>org.apache.tools.ant.types.selectors.ContainsSelector</code>
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| 309 | </li>
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| 310 | <li><a href="selectors.html#dateselect">Date Selector</a> with
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| 311 | classname <code>org.apache.tools.ant.types.selectors.DateSelector</code>
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| 312 | </li>
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| 313 | <li><a href="selectors.html#depthselect">Depth Selector</a> with
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| 314 | classname <code>org.apache.tools.ant.types.selectors.DepthSelector</code>
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| 315 | </li>
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| 316 | <li><a href="selectors.html#filenameselect">Filename Selector</a> with
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| 317 | classname <code>org.apache.tools.ant.types.selectors.FilenameSelector</code>
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| 318 | </li>
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| 319 | <li><a href="selectors.html#sizeselect">Size Selector</a> with
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| 320 | classname <code>org.apache.tools.ant.types.selectors.SizeSelector</code>
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| 321 | </li>
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| 322 | </ul>
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| 323 |
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| 324 | <p>Here is the example from the Depth Selector section rewritten
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| 325 | to use the selector through <code><custom></code>.</p>
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| 326 |
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| 327 | <blockquote><pre>
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| 328 | <fileset dir="${doc.path}" includes="**/*">
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| 329 | <custom classname="org.apache.tools.ant.types.selectors.DepthSelector">
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| 330 | <param name="max" value="1"/>
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| 331 | </custom>
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| 332 | </fileset>
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| 333 | </pre></blockquote>
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| 334 |
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| 335 | <p>Selects all files in the base directory and one directory below
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| 336 | that.</p>
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| 337 |
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| 338 | <h3><a name="filterreaders">Custom Filter Readers</a></h3>
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| 339 | <p>
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| 340 | Custom filter readers selectors are datatypes that implement
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| 341 | <code>org.apache.tools.ant.types.filters.ChainableReader</code>.
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| 342 | </p>
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| 343 | <p>There is only one method required.
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| 344 | <code>Reader chain(Reader reader)</code>.
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| 345 | This returns a reader that filters input from the specified
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| 346 | reader.
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| 347 | </p>
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| 348 | <p>
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| 349 | For example a filterreader that removes every second character
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| 350 | could be:
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| 351 | </p>
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| 352 | <blockquote>
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| 353 | <pre>
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| 354 | public class RemoveOddCharacters implements ChainableReader {
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| 355 | public Reader chain(Reader reader) {
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| 356 | return new BaseFilterReader(reader) {
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| 357 | int count = 0;
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| 358 | public int read() throws IOException {
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| 359 | while (true) {
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| 360 | int c = in.read();
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| 361 | if (c == -1) {
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| 362 | return c;
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| 363 | }
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| 364 | count++;
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| 365 | if ((count % 2) == 1) {
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| 366 | return c;
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| 367 | }
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| 368 | }
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| 369 | }
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| 370 | }
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| 371 | }
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| 372 | }
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| 373 | </pre>
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| 374 | </blockquote>
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| 375 | <p>
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| 376 | For line oriented filters it may be easier to extend
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| 377 | <code>ChainableFilterReader</code> an inner class of
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| 378 | <code>org.apache.tools.ant.filters.TokenFilter</code>.
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| 379 | </p>
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| 380 | <p>
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| 381 | For example a filter that appends the line number could be
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| 382 | </p>
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| 383 | <blockquote>
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| 384 | <pre>
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| 385 | public class AddLineNumber extends ChainableReaderFilter {
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| 386 | private void lineNumber = 0;
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| 387 | public String filter(String string) {
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| 388 | lineNumber++;
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| 389 | return "" + lineNumber + "\t" + string;
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| 390 | }
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| 391 | }
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| 392 | </pre>
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| 393 | </blockquote>
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| 394 |
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| 395 |
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| 396 | <hr></hr>
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| 397 | <p align="center">Copyright © 2003-2004 The Apache Software Foundation. All rights
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| 398 | Reserved.</p>
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| 399 | </body>
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| 400 | </html>
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| 401 |
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