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| <meta http-equiv="Content-Language" content="en-us"> |
| <title>Programming Selectors in Ant</title> |
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| <body> |
| <h2>Programming your own Selectors</h2> |
| |
| <h3>Selector Programming API</h3> |
| |
| <p>Want to define your own selectors? It's easy!</p> |
| |
| <p>First, pick the type of selector that you want to define. There |
| are three types, and a recipe for each one follows. Chances are |
| you'll want to work with the first one, Custom Selectors.</p> |
| |
| <h4>Custom Selectors</h4> |
| |
| <p>This is the category that Ant provides specifically for youto |
| define your own Selectors. Anywhere you want to use your selector |
| you use the <code><custom></code> element and specify |
| the class name of your selector within it. See the |
| <a href="selectors.html#customselect">Custom Selectors</a> |
| section of the Selector page for details. The |
| <code><custom></code> element can be used anywhere |
| the core selectors can be used. It can be contained within |
| <a href="selectors.html#selectcontainers">Selector Containers</a>, |
| for example.</p> |
| |
| <p>To create a new Custom Selector, you have to create a class that |
| implements |
| <code>org.apache.tools.ant.types.selectors.ExtendFileSelector</code>. |
| The easiest way to do that is through the convenience base class |
| <code>org.apache.tools.ant.types.selectors.BaseExtendSelector</code>, |
| which provides all of the methods for supporting |
| <code><param></code> tags. First, override the |
| <code>isSelected()</code> method, and optionally the |
| <code>verifySettings()</code> method. If your custom |
| selector requires parameters to be set, you can also override |
| the <code>setParameters()</code> method and interpret the |
| parameters that are passed in any way you like. Several of the |
| core selectors demonstrate how to do that because they can |
| also be used as custom selectors.</p> |
| |
| <p><i>Note: If you don't need to set variables on your selector |
| with the the embedded <code><param></code> |
| elements, your custom selector could just implement the |
| <code>org.apache.tools.ant.types.selectors.FileSelector</code> |
| interface rather than the full |
| <code>org.apache.tools.ant.types.selectors.ExtendFileSelector</code> |
| interface. Using the latter will give you the most flexibility, |
| though.</i></p> |
| |
| <p><i>Note: If you inherit from |
| <code>org.apache.tools.ant.types.selectors.BaseExtendSelector</code> |
| or |
| <code>org.apache.tools.ant.types.selectors.BaseSelector</code>, |
| any selector container will perform a validation pass before calling |
| the <code>isSelected()</code> method. Make sure that all |
| initialization is performed before the validation is done.</i></p> |
| |
| <h4>Core Selectors</h4> |
| |
| <p>These are the selectors used by Ant itself. To implement one of |
| these, you will have to alter some of the classes contained within |
| Ant.</p> |
| |
| <ul> |
| <li><p>First, create a class that implements |
| <code>org.apache.tools.ant.types.selectors.FileSelector</code>. |
| You can either choose to implement all methods yourself from |
| scratch, or you can extend |
| <code>org.apache.tools.ant.types.selectors.BaseSelector</code> |
| instead, a convenience class that provides reasonable default |
| behaviour for many methods.</p> |
| |
| <p>There is only one method required. |
| <code>public boolean isSelected(File basedir, String filename, |
| File file)</code> |
| is the real purpose of the whole exercise. It returns true |
| or false depending on whether the given file should be |
| selected from the list or not.</p> |
| |
| <p>If you are using |
| <code>org.apache.tools.ant.types.selectors.BaseSelector</code> |
| there are also some predefined behaviours you can take advantage |
| of. Any time you encounter a problem when setting attributes or |
| adding tags, you can call setError(String errmsg) and the class |
| will know that there is a problem. Then, at the top of your |
| <code>isSelected()</code> method call <code>validate()</code> and |
| a BuildException will be thrown with the contents of your error |
| message. The <code>validate()</code> method also gives you a |
| last change to check your settings for consistency because it |
| calls <code>verifySettings()</code>. Override this method and |
| call <code>setError()</code> within it if you detect any |
| problems in how your selector is set up.</p> |
| |
| <p>You may also want to override <code>toString()</code>.</p> |
| |
| <li><p>Put an <code>add</code> method for your selector in |
| <code>org.apache.tools.ant.types.selectors.SelectorContainer</code>. |
| This is an interface, so you will also have to add an implementation |
| for the method in the classes which implement it, namely |
| <code>org.apache.tools.ant.types.AbstractFileSet</code> and |
| <code>org.apache.tools.ant.types.selectors.BaseSelectorContainer</code>. |
| Once it is in there, it will be available everywhere that core |
| selectors are appropriate.</p> |
| </ul> |
| |
| <h4>Selector Containers</h4> |
| <p>Got an idea for a new Selector Container? Creating a new one is |
| no problem:</p> |
| <ul> |
| <li><p>Create a new class that implements |
| <code>org.apache.tools.ant.types.selectors.SelectorContainer</code>. |
| This will ensure that your new |
| Container can access any new selectors that come along. Again, there |
| is a convenience class available for you called |
| <code>org.apache.tools.ant.types.selectors.BaseSelectorContainer</code>. |
| </p> |
| <li><p>Implement the |
| <code>public boolean isSelected(String filename, File file)</code> |
| method to do the right thing. Chances are you'll want to iterate |
| over the selectors under you, so use |
| <code>selectorElements()</code> to get an iterator that will do |
| that.</p> |
| <li><p>Again, put an <code>add</code> method for your container in |
| <code>org.apache.tools.ant.types.selectors.SelectorContainer</code> |
| and its implementations |
| <code>org.apache.tools.ant.types.AbstractFileSet</code> and |
| <code>org.apache.tools.ant.types.selectors.BaseSelectorContainer</code>. |
| </p> |
| </ul> |
| |
| <hr> |
| <p align="center">Copyright © 2002 Apache Software |
| Foundation. All rights Reserved.</p> |
| |
| </body> |
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| </html> |
