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| <html> |
| |
| <head> |
| <meta http-equiv="Content-Language" content="en-us"> |
| <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><a name="writingowntask">Writing Your Own Task</a></h2> |
| <p>It is very easy to write your own task:</p> |
| <ol> |
| <li>Create a Java class that extends <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>For each attribute, write a <i>setter</i> 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"><sup>*</sup></a>. That is, to support an attribute named |
| <code>file</code> you create a method <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>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 end end tags), write a <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 <i>create</i>, <i>add</i> or |
| <i>addConfigured</i> 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>public void execute</code> method, with no arguments, that |
| throws a <code>BuildException</code>. This method implements the task |
| itself.</li> |
| </ol> |
| |
| <hr> |
| <p><a name="footnote-1">*</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 UnknownElement at parser time. |
| This UnknownElement gets placed in a list within a target |
| object, or recursively within another UnknownElement. |
| </li> |
| <li> |
| When the target is executed, each UnknownElement is invoked |
| using an <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 <code>id</code> 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>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>createXXX()</code> methods or |
| instantiated and added to this task via its <code>addXXX()</code> |
| methods, at run time. Child elements corresponding |
| to <code>addConfiguredXXX()</code> are created at this point but |
| the actual <code>addCondifgired</code> method is not called.</li> |
| |
| <li>All attributes of this task get set via their corresponding |
| <code>setXXX</code> methods, at runtime.</li> |
| |
| <li>The content character data sections inside the XML element |
| corresponding to this task is added to the task via its |
| <code>addText</code> method, at runtime.</li> |
| |
| <li>All attributes of all child elements get set via their corresponding |
| <code>setXXX</code> methods, at runtime.</li> |
| |
| <li>If child elements of the XML element corresponding to this task |
| have been created for <code>addConfiguredXXX()</code> methods, |
| those methods get invoked now.</li> |
| |
| <li><a name="execute"><code>execute()</code></a> is called at runtime. |
| If <code>target1</code> and <code>target2</code> both depend |
| on <code>target3</code>, then running |
| <code>'ant target1 target2'</code> will run all tasks in |
| <code>target3</code> twice.</li> |
| </ol> |
| |
| <h3><a name="set-magic">Conversions Ant will perform for attributes</a></h3> |
| |
| <p>Ant will always expand properties before it passes the value of an |
| attribute to the corresponding setter method. <b>Since Ant 1.8</b>, 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>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 |
| <i>true</i> if the value specified in the build file is one of |
| <code>true</code>, <code>yes</code>, or <code>on</code> and |
| <i>false</i> otherwise.</li> |
| |
| <li><code>char</code> or <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>int</code>, <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>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 basedir.</li> |
| |
| <li><code>org.apache.tools.ant.types.Resource</code> |
| <code>org.apache.tools.ant.types.Resource</code>, Ant will |
| resolve the string as a <code>java.io.File</code> as above, then |
| pass in as a <code>org.apache.tools.ant.types.resources.FileResource</code>. |
| <b>Since Ant 1.8</b> |
| </li> |
| |
| <li><code>org.apache.tools.ant.types.Path</code>, Ant will tokenize |
| the value specified in the build file, accepting <code>:</code> and |
| <code>;</code> as path separators. Relative path names will be |
| interpreted as relative to the project's basedir.</li> |
| |
| <li><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>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>org.apache.tools.ant.types.EnumeratedAttribute</code>, Ant |
| will invoke this classes <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>AddAsisRemove</code> class used in <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>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>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>As of 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>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><a name="nested-elements">Supporting nested elements</a></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>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. setter |
| methods for attributes, addText for nested text and |
| create/add/addConfigured methods for child elements).</p> |
| |
| <p>Now you have a 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>public NestedElement createInner()</code></li> |
| <li><code>public void addInner(NestedElement anInner)</code></li> |
| <li><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>NestedElement</code>, there are no restrictions on the type. |
| For the options 2 and 3, Ant has to create an instance of |
| <code>NestedInner</code> before it can pass it to the task, this |
| means, <code>NestedInner</code> must have a <code>public</code> no-arg |
| constructor or a <code>public</code> one-arg constructor |
| taking a Project 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>addInner</code> will receive |
| an object directly after the constructor has been called, while |
| <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 Java virtual machine.</p> |
| |
| <h3><a name="nestedtype">Nested Types</a></h3> |
| If your task needs to nest an arbitrary type that has been defined |
| using <code><typedef></code> you have two options. |
| <ol> |
| <li><code>public void add(Type type)</code></li> |
| <li><code>public void addConfigured(Type type)</code></li> |
| </ol> |
| The difference between 1 and 2 is the same as between 2 and 3 in the |
| previous section. |
| <p> |
| For example suppose one wanted to handle objects object of type |
| org.apache.tools.ant.taskdefs.condition.Condition, one may |
| have a class: |
| </p> |
| <blockquote> |
| <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> |
| </blockquote> |
| <p> |
| One may define and use this class like this: |
| </p> |
| <blockquote> |
| <pre> |
| <taskdef name="mytask" classname="MyTask" classpath="classes"/> |
| <typedef name="condition.equals" |
| classname="org.apache.tools.ant.taskdefs.conditions.Equals"/> |
| <mytask> |
| <condition.equals arg1="${debug}" arg2="true"/> |
| </mytask> |
| </pre> |
| </blockquote> |
| <p> |
| A more complicated example follows: |
| </p> |
| <blockquote> |
| <pre> |
| public class Sample { |
| public static class MyFileSelector implements FileSelector { |
| public void setAttrA(int a) {} |
| public void setAttrB(int b) {} |
| public void add(Path path) {} |
| public boolean isSelected(File basedir, String filename, File file) { |
| return true; |
| } |
| } |
| |
| interface MyInterface { |
| void setVerbose(boolean val); |
| } |
| |
| public static class BuildPath extends Path { |
| public BuildPath(Project project) { |
| super(project); |
| } |
| |
| public void add(MyInterface inter) {} |
| public void setUrl(String url) {} |
| } |
| |
| public static class XInterface implements MyInterface { |
| public void setVerbose(boolean x) {} |
| public void setCount(int c) {} |
| } |
| } |
| </pre> |
| </blockquote> |
| <p> |
| This class defines a number of static classes that implement/extend |
| Path, MyFileSelector and MyInterface. These may be defined and used |
| as follows: |
| </p> |
| <pre> |
| <blockquote> |
| <typedef name="myfileselector" classname="Sample$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> |
| </blockquote> |
| </pre> |
| |
| <h3><a name="taskcontainer">TaskContainer</a></h3> |
| |
| <p>The <code>TaskContainer</code> consists of a single method, |
| <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>execute</code> method gets |
| invoked, but not before that.</p> |
| |
| <p>When we <a href="#execute">said</a> <code>execute</code> would be |
| called, we lied ;-). In fact, Ant will call the <code>perform</code> |
| method in <code>org.apache.tools.ant.Task</code>, which in turn calls |
| <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>perform</code> on these instances instead of |
| <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> |
| <blockquote> |
| <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> |
| </blockquote> |
| <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> |
| <blockquote> |
| <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> |
| </blockquote> |
| |
| <h3>Example 2</h3> |
| To use a task directly from the buildfile which created it, place the |
| <code><taskdef></code> declaration inside a target |
| <i>after the compilation</i>. Use the <code>classpath</code> attribute of |
| <code><taskdef></code> to point to where the code has just been |
| compiled. |
| <blockquote> |
| <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> |
| </blockquote> |
| |
| <p>Another way to add a task (more permanently), is to add the task name and |
| implementing class name to the <code>default.properties</code> file in the |
| <code>org.apache.tools.ant.taskdefs</code> |
| package. Then you can use it as if it were a built-in task.</p> |
| |
| <hr> |
| <h2><a name="buildevents">Build Events</a></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>Project</code> object. You can then call the |
| <code>addBuildListener</code> method to add your listener to the project. Your listener must implement |
| the <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. Ant 1.6.2 |
| introduces an extension of the BuildListener interface named |
| SubBuildListener 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 BuildListener (and register the |
| listener, of course).</p> |
| |
| <p>If you wish to attach a listener from the command line you may use the |
| <code>-listener</code> option. For example:</p> |
| <blockquote> |
| <pre>ant -listener org.apache.tools.ant.XmlLogger</pre> |
| </blockquote> |
| <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><b>Note: </b>A listener must not access System.out and System.err 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 Java VM to run out of Stack space. A logger, also, may |
| not access System.out and System.err directly. It must use the streams with which it has |
| been configured.</p> |
| |
| <p><b>Note2:</b> All methods of a BuildListener 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> |
| |
| <hr> |
| <h2><a name="integration">Source code integration</a></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="http://www.apache.org/foundation/getinvolved.html">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="http://ant.apache.org/ant_task_guidelines.html">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> |
| |