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| <html lang="en"> |
| |
| <head> |
| <link rel="stylesheet" type="text/css" href="stylesheets/style.css"> |
| <title>Writing Your Own Task</title> |
| </head> |
| |
| <body> |
| <h1>Developing with Apache Ant</h1> |
| |
| <h2 id="writingowntask">Writing Your Own Task</h2> |
| <p>It is very easy to write your own task:</p> |
| <ol> |
| <li>Create a Java class that extends <code class="code">org.apache.tools.ant.Task</code> |
| or <a href="base_task_classes.html">another class</a> that was designed to be extended.</li> |
| |
| <li id="footnote-1-back">For each attribute, write a <em>setter</em> method. The setter method |
| must be a <code>public void</code> method that takes a single argument. The name of the method |
| must begin with <code>set</code>, followed by the attribute name, with the first character of |
| the name in uppercase, and the rest in lowercase<a href="#footnote-1">*</a>. That is, to |
| support an attribute named <var>file</var> you create a |
| method <code class="code">setFile</code>. Depending on the type of the argument, Ant will |
| perform some conversions for you, see <a href="#set-magic">below</a>.</li> |
| |
| <li>If your task shall contain other tasks as nested elements |
| (like <a href="Tasks/parallel.html"><code>parallel</code></a>), your class must implement the |
| interface <code class="code">org.apache.tools.ant.TaskContainer</code>. If you do so, your task |
| can not support any other nested elements. See <a href="#taskcontainer">below</a>.</li> |
| |
| <li>If the task should support character data (text nested between the start and end tags), write |
| a <code class="code">public void addText(String)</code> method. Note that Ant |
| does <strong>not</strong> expand properties on the text it passes to the task.</li> |
| |
| <li>For each nested element, write a <em>create</em>, <em>add</em> or <em>addConfigured</em> |
| method. A create method must be a <code>public</code> method that takes no arguments and |
| returns an <code>Object</code> type. The name of the create method must begin |
| with <code>create</code>, followed by the element name. An add (or addConfigured) method must be |
| a <code>public void</code> method that takes a single argument of an <code>Object</code> type |
| with a no-argument constructor. The name of the add (addConfigured) method must begin |
| with <code>add</code> (<code>addConfigured</code>), followed by the element name. For a more |
| complete discussion see <a href="#nested-elements">below</a>.</li> |
| |
| <li>Write a <code class="code">public void execute()</code> method, with no arguments, that throws |
| a <code>BuildException</code>. This method implements the task itself.</li> |
| </ol> |
| |
| <hr/> |
| <p id="footnote-1"><a href="#footnote-1-back">*</a> Actually the case of the letters after the first |
| one doesn't really matter to Ant, using all lower case is a good convention, though.</p> |
| |
| <h3>The Life-cycle of a Task</h3> |
| <ol> |
| <li>The xml element that contains the tag corresponding to the task gets converted to |
| an <code class="code">UnknownElement</code> at parse time. |
| This <code class="code">UnknownElement</code> gets placed in a list within a target object, or |
| recursively within another <code class="code">UnknownElement</code>. |
| </li> |
| |
| <li>When the target is executed, each <code class="code">UnknownElement</code> is invoked using |
| an <code class="code">perform()</code> method. This instantiates the task. This means that tasks |
| only gets instantiated at run time. |
| </li> |
| |
| <li>The task gets references to its project and location inside the buildfile via its |
| inherited <code>project</code> and <code>location</code> variables.</li> |
| |
| <li>If the user specified an <var>id</var> attribute to this task, the project registers a |
| reference to this newly created task, at run time.</li> |
| |
| <li>The task gets a reference to the target it belongs to via its inherited <code>target</code> |
| variable.</li> |
| |
| <li><code class="code">init()</code> is called at run time.</li> |
| |
| <li>All child elements of the XML element corresponding to this task are created via this |
| task's <code class="code">createXXX()</code> methods or instantiated and added to this task via |
| its <code class="code">addXXX()</code> methods, at run time. Child elements corresponding |
| to <code class="code">addConfiguredXXX()</code> are created at this point but the |
| actual <em>addConfigured</em> method is not called.</li> |
| |
| <li>All attributes of this task get set via their corresponding <code class="code">setXXX()</code> |
| methods, at run time.</li> |
| |
| <li>The content character data sections inside the XML element corresponding to this task is added |
| to the task via its <code class="code">addText()</code> method, at run time.</li> |
| |
| <li>All attributes of all child elements get set via their |
| corresponding <code class="code">setXXX()</code> methods, at run time.</li> |
| |
| <li>If child elements of the XML element corresponding to this task have been created |
| for <code class="code">addConfiguredXXX()</code> methods, those methods get invoked now.</li> |
| |
| <li id="execute"><code class="code">execute()</code> is called at run time. If <q>target1</q> |
| and <q>target2</q> both depend on <q>target3</q>, then running <kbd>ant target1 target2</kbd> |
| will run all tasks in <q>target3</q> twice.</li> |
| </ol> |
| |
| <h3 id="set-magic">Conversions Ant will perform for attributes</h3> |
| |
| <p>Ant will always expand properties before it passes the value of an attribute to the corresponding |
| setter method. <em>Since Ant 1.8</em>, it is possible to <a href="Tasks/propertyhelper.html">extend |
| Ant's property handling</a> such that a non-string Object may be the result of the evaluation of a |
| string containing a single property reference. These will be assigned directly via setter methods of |
| matching type. Since it requires some beyond-the-basics intervention to enable this behavior, it may |
| be a good idea to flag attributes intended to permit this usage paradigm.</p> |
| |
| <p>The most common way to write an attribute setter is to use |
| a <code class="code">java.lang.String</code> argument. In this case Ant will pass the literal value |
| (after property expansion) to your task. But there is more! If the argument of you setter method |
| is</p> |
| |
| <ul> |
| <li><code>boolean</code>, your method will be passed the value <q>true</q> if the value specified |
| in the build file is one of <q>true</q>, <q>yes</q>, or <q>on</q> and <q>false</q> |
| otherwise.</li> |
| |
| <li><code>char</code> or <code class="code">java.lang.Character</code>, your method will be passed |
| the first character of the value specified in the build file.</li> |
| |
| <li>any other primitive type (<code class="code">int</code>, <code class="code">short</code> and |
| so on), Ant will convert the value of the attribute into this type, thus making sure that you'll |
| never receive input that is not a number for that attribute.</li> |
| |
| <li><code class="code">java.io.File</code>, Ant will first determine whether the value given in |
| the build file represents an absolute path name. If not, Ant will interpret the value as a path |
| name relative to the project's <var>basedir</var>.</li> |
| |
| <li><code class="code">org.apache.tools.ant.types.Resource</code>, Ant will resolve the string as |
| a <code class="code">java.io.File</code> as above, then pass in as |
| a <code class="code">org.apache.tools.ant.types.resources.FileResource</code>. <em>Since Ant |
| 1.8</em></li> |
| |
| <li><code class="code">org.apache.tools.ant.types.Path</code>, Ant will tokenize the value |
| specified in the build file, accepting <q>:</q> and <q>;</q> as path separators. Relative path |
| names will be interpreted as relative to the project's <var>basedir</var>.</li> |
| |
| <li><code class="code">java.lang.Class</code>, Ant will interpret the value given in the build |
| file as a Java class name and load the named class from the system class loader.</li> |
| |
| <li>any other type that has a constructor with a single <code class="code">String</code> argument, |
| Ant will use this constructor to create a new instance from the value given in the build |
| file.</li> |
| |
| <li>A subclass of <code class="code">org.apache.tools.ant.types.EnumeratedAttribute</code>, Ant |
| will invoke this class's <code class="code">setValue</code> method. Use this if your task |
| should support enumerated attributes (attributes with values that must be part of a predefined |
| set of values). See <code>org/apache/tools/ant/taskdefs/FixCRLF.java</code> and the |
| inner <code class="code">AddAsisRemove</code> class used in <code class="code">setCr</code> for |
| an example.</li> |
| |
| <li>A (Java 5) enumeration, Ant will call the setter with the enum constant matching the value |
| given in the build file. This is easier than using <code class="code">EnumeratedAttribute</code> |
| and can result in cleaner code, but of course your task will not run on JDK 1.4 or earlier. Note |
| that any override of <code class="code">toString()</code> in the enumeration is ignored; the |
| build file must use the declared name (see <code>Enum.getName()</code>). You may wish to use |
| lowercase enum constant names, in contrast to usual Java style, to look better in build |
| files. <em>Since Ant 1.7.0</em></li> |
| </ul> |
| |
| <p>What happens if more than one setter method is present for a given attribute? A method taking |
| a <code class="code">String</code> argument will always lose against the more specific methods. If |
| there are still more setters Ant could chose from, only one of them will be called, but we don't |
| know which, this depends on the implementation of your Java virtual machine.</p> |
| |
| <h3 id="nested-elements">Supporting nested elements</h3> |
| |
| <p>Let's assume your task shall support nested elements with the name <code>inner</code>. First of |
| all, you need a class that represents this nested element. Often you simply want to use one of |
| Ant's classes like <code class="code">org.apache.tools.ant.types.FileSet</code> to support |
| nested <code>fileset</code> elements.</p> |
| |
| <p>Attributes of the nested elements or nested child elements of them will be handled using the same |
| mechanism used for tasks (i.e. <em>setter</em> methods for |
| attributes, <code class="code">addText()</code> for nested text |
| and <em>create</em>/<em>add</em>/<em>addConfigured</em> methods for child elements).</p> |
| |
| <p>Now you have a class <code class="code">NestedElement</code> that is supposed to be used for your |
| nested <code><inner></code> elements, you have three options:</p> |
| |
| <ol> |
| <li><code class="code">public NestedElement createInner()</code></li> |
| <li><code class="code">public void addInner(NestedElement anInner)</code></li> |
| <li><code class="code">public void addConfiguredInner(NestedElement anInner)</code></li> |
| </ol> |
| |
| <p>What is the difference?</p> |
| |
| <p>Option 1 makes the task create the instance of <code class="code">NestedElement</code>, there are |
| no restrictions on the type. For the options 2 and 3, Ant has to create an instance |
| of <code class="code">NestedInner</code> before it can pass it to the task, this |
| means, <code class="code">NestedInner</code> must have a <code>public</code> no-arg constructor or |
| a <code>public</code> one-arg constructor taking a <code class="code">Project</code> class as a |
| parameter. This is the only difference between options 1 and 2.</p> |
| |
| <p>The difference between 2 and 3 is what Ant has done to the object before it passes it to the |
| method. <code class="code">addInner()</code> will receive an object directly after the constructor |
| has been called, while <code class="code">addConfiguredInner()</code> gets the object <em>after</em> |
| the attributes and nested children for this new object have been handled.</p> |
| |
| <p>What happens if you use more than one of the options? Only one of the methods will be called, |
| but we don't know which, this depends on the implementation of your JVM.</p> |
| |
| <h3 id="nestedtype">Nested Types</h3> |
| <p>If your task needs to nest an arbitrary type that has been defined |
| using <code><typedef></code> you have two options.</p> |
| <ol> |
| <li><code class="code">public void add(Type type)</code></li> |
| <li><code class="code">public void addConfigured(Type type)</code></li> |
| </ol> |
| <p>The difference between 1 and 2 is the same as between 2 and 3 in the previous section.</p> |
| <p>For example suppose one wanted to handle objects object of |
| type <code class="code">org.apache.tools.ant.taskdefs.condition.Condition</code>, one may have a |
| class:</p> |
| <pre> |
| public class MyTask extends Task { |
| private List conditions = new ArrayList(); |
| public void add(Condition c) { |
| conditions.add(c); |
| } |
| public void execute() { |
| // iterator over the conditions |
| } |
| }</pre> |
| <p>One may define and use this class like this:</p> |
| <pre> |
| <taskdef name="mytask" classname="MyTask" classpath="classes"/> |
| <typedef name="condition.equals" |
| classname="org.apache.tools.ant.taskdefs.conditions.Equals"/> |
| <mytask> |
| <condition.equals arg1="${debug}" arg2="true"/> |
| </mytask></pre> |
| <p>A more complicated example follows:</p> |
| <pre> |
| public class Sample { |
| public static class MyFileSelector implements FileSelector { |
| public void setAttrA(int a) {} |
| public void setAttrB(int b) {} |
| public void add(Path path) {} |
| public boolean isSelected(File basedir, String filename, File file) { |
| return true; |
| } |
| } |
| |
| interface MyInterface { |
| void setVerbose(boolean val); |
| } |
| |
| public static class BuildPath extends Path { |
| public BuildPath(Project project) { |
| super(project); |
| } |
| |
| public void add(MyInterface inter) {} |
| public void setUrl(String url) {} |
| } |
| |
| public static class XInterface implements MyInterface { |
| public void setVerbose(boolean x) {} |
| public void setCount(int c) {} |
| } |
| }</pre> |
| <p>This class defines a number of static classes that |
| implement/extend <code class="code">Path</code>, <code class="code">MyFileSelector</code> |
| and <code class="code">MyInterface</code>. These may be defined and used as follows:</p> |
| <pre> |
| <typedef name="myfileselector" classname="Sample$MyFileSelector" |
| classpath="classes" loaderref="classes"/> |
| <typedef name="buildpath" classname="Sample$BuildPath" |
| classpath="classes" loaderref="classes"/> |
| <typedef name="xinterface" classname="Sample$XInterface" |
| classpath="classes" loaderref="classes"/> |
| |
| <copy todir="copy-classes"> |
| <fileset dir="classes"> |
| <myfileselector attra="10" attrB="-10"> |
| <buildpath path="." url="abc"> |
| <xinterface count="4"/> |
| </buildpath> |
| </myfileselector> |
| </fileset> |
| </copy></pre> |
| |
| <h3 id="taskcontainer">TaskContainer</h3> |
| |
| <p>The <code class="code">TaskContainer</code> consists of a single |
| method, <code class="code">addTask</code> that basically is the same as |
| an <a href="#nested-elements">add method</a> for nested elements. The task instances will be |
| configured (their attributes and nested elements have been handled) when your |
| task's <code class="code">execute</code> method gets invoked, but not before that.</p> |
| |
| <p>When we <a href="#execute">said</a> <code class="code">execute</code> would be called, we lied |
| ;-). In fact, Ant will call the <code class="code">perform</code> method |
| in <code class="code">org.apache.tools.ant.Task</code>, which in turn |
| calls <code class="code">execute</code>. This method makes sure that <a href="#buildevents">Build |
| Events</a> will be triggered. If you execute the task instances nested into your task, you should |
| also invoke <code class="code">perform</code> on these instances instead |
| of <code class="code">execute</code>.</p> |
| |
| <h3>Example</h3> |
| <p>Let's write our own task, which prints a message on the <code>System.out</code> stream. The task |
| has one attribute, called <code>message</code>.</p> |
| |
| <pre> |
| package com.mydomain; |
| |
| import org.apache.tools.ant.BuildException; |
| import org.apache.tools.ant.Task; |
| |
| public class MyVeryOwnTask extends Task { |
| private String msg; |
| |
| // The method executing the task |
| public void execute() throws BuildException { |
| System.out.println(msg); |
| } |
| |
| // The setter for the "message" attribute |
| public void setMessage(String msg) { |
| this.msg = msg; |
| } |
| }</pre> |
| |
| <p>It's really this simple ;-)</p> |
| <p>Adding your task to the system is rather simple too:</p> |
| <ol> |
| <li>Make sure the class that implements your task is in the classpath when starting Ant.</li> |
| <li>Add a <code><taskdef></code> element to your project. This actually adds your task to |
| the system.</li> |
| <li>Use your task in the rest of the buildfile.</li> |
| </ol> |
| |
| <h3>Example</h3> |
| |
| <pre> |
| <?xml version="1.0"?> |
| |
| <project name="OwnTaskExample" default="main" basedir="."> |
| <taskdef name="mytask" classname="com.mydomain.MyVeryOwnTask"/> |
| |
| <target name="main"> |
| <mytask message="Hello World! MyVeryOwnTask works!"/> |
| </target> |
| </project></pre> |
| |
| <h3>Example 2</h3> |
| <p>To use a task directly from the buildfile which created it, place |
| the <code><taskdef></code> declaration inside a target <em>after the compilation</em>. Use |
| the <var>classpath</var> attribute of <code><taskdef></code> to point to where the code has |
| just been compiled.</p> |
| |
| <pre> |
| <?xml version="1.0"?> |
| |
| <project name="OwnTaskExample2" default="main" basedir="."> |
| |
| <target name="build" > |
| <mkdir dir="build"/> |
| <javac srcdir="source" destdir="build"/> |
| </target> |
| |
| <target name="declare" depends="build"> |
| <taskdef name="mytask" |
| classname="com.mydomain.MyVeryOwnTask" |
| classpath="build"/> |
| </target> |
| |
| <target name="main" depends="declare"> |
| <mytask message="Hello World! MyVeryOwnTask works!"/> |
| </target> |
| </project></pre> |
| |
| <p>Another way to add a task (more permanently) is to add the task name and implementing class name |
| to the <samp>default.properties</samp> file in |
| the <code class="code">org.apache.tools.ant.taskdefs</code> package. Then you can use it as if it |
| were a built-in task.</p> |
| |
| <hr/> |
| <h2 id="buildevents">Build Events</h2> |
| <p>Ant is capable of generating build events as it performs the tasks necessary to build a project. |
| Listeners can be attached to Ant to receive these events. This capability could be used, for |
| example, to connect Ant to a GUI or to integrate Ant with an IDE.</p> |
| <p>To use build events you need to create an ant <code class="code">Project</code> object. You can |
| then call the <code class="code">addBuildListener</code> method to add your listener to the |
| project. Your listener must implement |
| the <code class="code">org.apache.tools.antBuildListener</code> interface. The listener will receive |
| BuildEvents for the following events</p> |
| <ul> |
| <li>Build started</li> |
| <li>Build finished</li> |
| <li>Target started</li> |
| <li>Target finished</li> |
| <li>Task started</li> |
| <li>Task finished</li> |
| <li>Message logged</li> |
| </ul> |
| |
| <p>If the build file invokes another build file |
| via <a href="Tasks/ant.html"><code><ant></code></a> |
| or <a href="Tasks/subant.html"><code><subant></code></a> or |
| uses <a href="Tasks/antcall.html"><code><antcall></code></a>, you are creating a new Ant |
| "project" that will send target and task level events of its own but never sends build |
| started/finished events. <em>Since Ant 1.6.2</em>, <code class="code">BuildListener</code> interface |
| has an extension named <code class="code">SubBuildListener</code> that will receive two new events |
| for</p> |
| <ul> |
| <li>SubBuild started</li> |
| <li>SubBuild finished</li> |
| </ul> |
| <p>If you are interested in those events, all you need to do is to implement the new interface |
| instead of <code class="code">BuildListener</code> (and register the listener, of course).</p> |
| |
| <p>If you wish to attach a listener from the command line you may use the <kbd>-listener</kbd> |
| option. For example:</p> |
| |
| <pre class="input">ant -listener org.apache.tools.ant.XmlLogger</pre> |
| |
| <p>will run Ant with a listener that generates an XML representation of the build progress. This |
| listener is included with Ant, as is the default listener, which generates the logging to standard |
| output.</p> |
| |
| <p><strong>Note</strong>: A listener must not access <code class="code">System.out</code> |
| and <code class="code">System.err</code> directly since output on these streams is redirected by |
| Ant's core to the build event system. Accessing these streams can cause an infinite loop in |
| Ant. Depending on the version of Ant, this will either cause the build to terminate or the JVM to |
| run out of Stack space. A logger, also, may not access <code class="code">System.out</code> |
| and <code class="code">System.err</code> directly. It must use the streams with which it has been |
| configured.</p> |
| |
| <p><strong>Note</strong>: All methods of a <code class="code">BuildListener</code> except for the |
| "Build Started" and "Build Finished" events may occur on several threads simultaneously—for |
| example while Ant is executing a <code><parallel></code> task.</p> |
| |
| <h3>Example</h3> |
| <p>Writing an adapter to your favourite log library is very easy. Just implement |
| the <code class="code">BuildListener</code> interface, instantiate your logger and delegate the |
| message to that instance.</p> |
| <p>When starting your build provide your adapter class and the log library to the build classpath |
| and activate your logger via <kbd>-listener</kbd> option as described above.</p> |
| |
| <pre> |
| public class MyLogAdapter implements BuildListener { |
| |
| private MyLogger getLogger() { |
| final MyLogger log = MyLoggerFactory.getLogger(Project.class.getName()); |
| return log; |
| } |
| |
| @Override |
| public void buildStarted(final BuildEvent event) { |
| final MyLogger log = getLogger(); |
| log.info("Build started."); |
| } |
| |
| @Override |
| public void buildFinished(final BuildEvent event) { |
| final MyLogger logger = getLogger(); |
| MyLogLevelEnum loglevel = ... // map event.getPriority() to enum via Project.MSG_* constants |
| boolean allOK = event.getException() == null; |
| String logmessage = ... // create log message using data of the event and the message invoked |
| logger.log(loglevel, logmessage); |
| } |
| |
| // implement all methods in that way |
| }</pre> |
| |
| <hr/> |
| <h2 id="integration">Source code integration</h2> |
| |
| <p>The other way to extend Ant through Java is to make changes to existing tasks, which is |
| positively encouraged. Both changes to the existing source and new tasks can be incorporated back |
| into the Ant codebase, which benefits all users and spreads the maintenance load around.</p> |
| |
| <p>Please consult the <a href="https://www.apache.org/foundation/getinvolved.html" |
| target="_top">Getting Involved</a> pages on the Apache web site for details on how to fetch the |
| latest source and how to submit changes for reincorporation into the source tree.</p> |
| |
| <p>Ant also has some <a href="https://ant.apache.org/ant_task_guidelines.html" target="_top">task |
| guidelines</a> which provides some advice to people developing and testing tasks. Even if you intend |
| to keep your tasks to yourself, you should still read this as it should be informative.</p> |
| |
| </body> |
| </html> |