This document provides a step by step tutorial for writing +tasks.
+Ant builds itself, we are using Ant too (why we would write +a task if not? :-) therefore we should use Ant for our build.
+
We choose a directory as root directory. All things will be done +here if I say nothing different. I will reference this directory +as root-directory of our project. In this root-directory we +create a text file names build.xml. What should Ant do for us? +
+<?xml version="1.0" encoding="ISO-8859-1"?> +<project name="MyTask" basedir="." default="jar"> + + <target name="clean" description="Delete all generated files"> + <delete dir="classes"/> + <delete file="MyTasks.jar"/> + </target> + + <target name="compile" description="Compiles the Task"> + <javac srcdir="src" destdir="classes"/> + </target> + + <target name="jar" description="JARs the Task"> + <jar destfile="MyTask.jar" basedir="classes"/> + </target> + +</project> ++ +This buildfile uses often the same value (src, classes, MyTask.jar), so we should rewrite that +using <property>s. On second there are some handicaps: <javac> requires that the destination +directory exists; a call of "clean" with a non existing classes directory will fail; "jar" requires +the execution of some steps bofore. So the refactored code is: + +
+<?xml version="1.0" encoding="ISO-8859-1"?>
+<project name="MyTask" basedir="." default="jar">
+
+ <property name="src.dir" value="src"/>
+ <property name="classes.dir" value="classes"/>
+
+ <target name="clean" description="Delete all generated files">
+ <delete dir="${classes.dir}" failonerror="false"/>
+ <delete file="${ant.project.name}.jar"/>
+ </target>
+
+ <target name="compile" description="Compiles the Task">
+ <mkdir dir="${classes.dir}"/>
+ <javac srcdir="${src.dir}" destdir="${classes.dir}"/>
+ </target>
+
+ <target name="jar" description="JARs the Task" depends="compile">
+ <jar destfile="${ant.project.name}.jar" basedir="${classes.dir}"/>
+ </target>
+
+</project>
+
+ant.project.name is one of the
+
+build-in properties [1] of Ant.
+
+
+
+
+public class HelloWorld {
+ public void execute() {
+ System.out.println("Hello World");
+ }
+}
+
+and we can compile and jar it with ant (default target is "jar" and via
+its depends-clause the "compile" is executed before).
+
+
+
+
+But after creating the jar we want to use our new Task. Therefore we need a +new target "use". Before we can use our new task we have to declare it with + +<taskdef> [2]. And for easier process we change the default clause: +
+<?xml version="1.0" encoding="ISO-8859-1"?>
+<project name="MyTask" basedir="." default="use">
+
+ ...
+
+ <target name="use" description="Use the Task" depends="jar">
+ <taskdef name="helloworld" classname="HelloWorld" classpath="${ant.project.name}.jar"/>
+ <helloworld/>
+ </target>
+
+</project>
+
+
+Important is the classpath-attribute. Ant searches in its /lib directory for
+tasks and our task isnīt there. So we have to provide the right location.
+
+Now we can type in ant and all should work ... +
+Buildfile: build.xml + +compile: + [mkdir] Created dir: C:\tmp\anttests\MyFirstTask\classes + [javac] Compiling 1 source file to C:\tmp\anttests\MyFirstTask\classes + +jar: + [jar] Building jar: C:\tmp\anttests\MyFirstTask\MyTask.jar + +use: +[helloworld] Hello World + +BUILD SUCCESSFUL +Total time: 3 seconds ++ + + + +
Our class has nothing to do with Ant. It extends no superclass and implements +no interface. How does Ant know to integrate? Via name convention: our class provides +a method with signature public void execute(). This class is wrapped by Antīs +org.apache.tools.ant.TaskAdapter which is a task and uses reflection for +setting a reference to the project and calling the execute() method.
+ +Setting a reference to the project? Could be interesting. The Project class +gives us some nice abilities: access to Antīs logging facilities getting and setting +properties and much more. So we try to use that class: +
+import org.apache.tools.ant.Project;
+
+public class HelloWorld {
+
+ private Project project;
+
+ public void setProject(Project proj) {
+ project = proj;
+ }
+
+ public void execute() {
+ String message = project.getProperty("ant.project.name");
+ project.log("Here is project '" + message + "'.", Project.MSG_INFO);
+ }
+}
+
+and the execution with ant will show us the expected
++use: +Here is project 'MyTask'. ++ + + +
Ok, that works ... But usually you will extend org.apache.tools.ant.Task. +That class is integrated in Ant, getīs the project-reference, provides documentation +fiels, provides easier access to the logging facility and (very useful) gives you +the exact location where in the buildfile this task instance is used.
+ +Oki-doki - letīs us use some of these: +
+import org.apache.tools.ant.Task;
+
+public class HelloWorld extends Task {
+ public void execute() {
+ // use of the reference to Project-instance
+ String message = getProject().getProperty("ant.project.name");
+
+ // Taskīs log method
+ log("Here is project '" + message + "'.");
+
+ // where this task is used?
+ log("I am used in: " + getLocation() );
+ }
+}
+
+which gives us when running
++use: +[helloworld] Here is project 'MyTask'. +[helloworld] I am used in: C:\tmp\anttests\MyFirstTask\build.xml:23: ++ + + +
Now we want to specify the text of our message (it seems that we are +rewriting the <echo/> task :-). First we well do that with an attribute. +It is very easy - for each attribute provide a public void set<attributename>(<type> +newValue) method and Ant will do the rest via reflection.
+
+import org.apache.tools.ant.Task;
+import org.apache.tools.ant.BuildException;
+
+public class HelloWorld extends Task {
+
+ String message;
+ public void setMessage(String msg) {
+ message = msg;
+ }
+
+ public void execute() {
+ if (message==null) {
+ throw new BuildException("No message set.");
+ }
+ log(message);
+ }
+
+}
+
+Oh, whatīs that in execute()? Throw a BuildException? Yes, thatīs the usual +way to show Ant that something important is missed and complete build should fail. The +string provided there is written as build-failes-message. Here itīs necessary because +the log() method canīt handle a null value as parameter and throws a NullPointerException. +(Of course you can initialize the message with a default string.)
+ +After that we have to modify our buildfile: +
+ <target name="use" description="Use the Task" depends="jar">
+ <taskdef name="helloworld"
+ classname="HelloWorld"
+ classpath="${ant.project.name}.jar"/>
+ <helloworld message="Hello World"/>
+ </target>
+
+Thatīs all.
+
+Some background for working with attributes: Ant supports any of these datatypes as +arguments of the set-method:
Maybe you have used the <echo> task in a way like <echo>Hello World</echo>. +For that you have to provide a public void addText(String text) method. +
+...
+public class HelloWorld extends Task {
+ ...
+ public void addText(String text) {
+ message = text;
+ }
+ ...
+}
+
+But here properties are not resolved! For resolving properties we have to use
+Projectīs replaceProperties(String propname) : String method which takes the
+property name as argument and returns its value (or ${propname} if not set).
+
+
+
+There are several ways for inserting the ability of handling nested elements. See +the Manual [4] for other. +We use the first way of the three described ways. There are several steps for that:
+import java.util.Vector;
+import java.util.Iterator;
+...
+ public void execute() {
+ if (message!=null) log(message);
+ for (Iterator it=messages.iterator(); it.hasNext(); ) { // 4
+ Message msg = (Message)it.next();
+ log(msg.getMsg());
+ }
+ }
+
+
+ Vector messages = new Vector(); // 2
+
+ public Message createMessage() { // 3
+ Message msg = new Message();
+ messages.add(msg);
+ return msg;
+ }
+
+ public class Message { // 1
+ public Message() {}
+
+ String msg;
+ public void setMsg(String msg) { this.msg = msg; }
+ public String getMsg() { return msg; }
+ }
+...
+
+Then we can use the new nested element. But where is xml-name for that defined? +The mapping XML-name : classname is defined in the factory method: +public classname createXML-name(). Therefore we write in +the buildfile +
+ <helloworld> + <message msg="Nested Element 1"/> + <message msg="Nested Element 2"/> + </helloworld> ++ + + +
For recapitulation now a little refactored buildfile: +
+<?xml version="1.0" encoding="ISO-8859-1"?>
+<project name="MyTask" basedir="." default="use">
+
+ <property name="src.dir" value="src"/>
+ <property name="classes.dir" value="classes"/>
+
+ <target name="clean" description="Delete all generated files">
+ <delete dir="${classes.dir}" failonerror="false"/>
+ <delete file="${ant.project.name}.jar"/>
+ </target>
+
+ <target name="compile" description="Compiles the Task">
+ <mkdir dir="${classes.dir}"/>
+ <javac srcdir="${src.dir}" destdir="${classes.dir}"/>
+ </target>
+
+ <target name="jar" description="JARs the Task" depends="compile">
+ <jar destfile="${ant.project.name}.jar" basedir="${classes.dir}"/>
+ </target>
+
+
+ <target name="use.init"
+ description="Taskdef the HelloWorld-Task"
+ depends="jar">
+ <taskdef name="helloworld"
+ classname="HelloWorld"
+ classpath="${ant.project.name}.jar"/>
+ </target>
+
+
+ <target name="use.without"
+ description="Use without any"
+ depends="use.init">
+ <helloworld/>
+ </target>
+
+ <target name="use.message"
+ description="Use with attribute 'message'"
+ depends="use.init">
+ <helloworld message="attribute-text"/>
+ </target>
+
+ <target name="use.fail"
+ description="Use with attribute 'fail'"
+ depends="use.init">
+ <helloworld fail="true"/>
+ </target>
+
+ <target name="use.nestedText"
+ description="Use with nested text"
+ depends="use.init">
+ <helloworld>nested-text</helloworld>
+ </target>
+
+ <target name="use.nestedElement"
+ description="Use with nested 'message'"
+ depends="use.init">
+ <helloworld>
+ <message msg="Nested Element 1"/>
+ <message msg="Nested Element 2"/>
+ </helloworld>
+ </target>
+
+
+ <target name="use"
+ description="Try all (w/out use.fail)"
+ depends="use.without,use.message,use.nestedText,use.nestedElement"
+ />
+
+</project>
+
+
+And the code of the task:
+
+import org.apache.tools.ant.Task;
+import org.apache.tools.ant.BuildException;
+import java.util.Vector;
+import java.util.Iterator;
+
+/**
+ * The task of the tutorial.
+ * Printīs a message or let the build fail.
+ * @author Jan Matčrne
+ * @since 2003-08-19
+ */
+public class HelloWorld extends Task {
+
+
+ /** The message to print. As attribute. */
+ String message;
+ public void setMessage(String msg) {
+ message = msg;
+ }
+
+ /** Should the build fail? Defaults to false. As attribute. */
+ boolean fail = false;
+ public void setFail(boolean b) {
+ fail = b;
+ }
+
+ /** Support for nested text. */
+ public void addText(String text) {
+ message = text;
+ }
+
+
+ /** Do the work. */
+ public void execute() {
+ // handle attribute 'fail'
+ if (fail) throw new BuildException("Fail requested.");
+
+ // handle attribute 'message' and nested text
+ if (message!=null) log(message);
+
+ // handle nested elements
+ for (Iterator it=messages.iterator(); it.hasNext(); ) {
+ Message msg = (Message)it.next();
+ log(msg.getMsg());
+ }
+ }
+
+
+ /** Store nested 'message's. */
+ Vector messages = new Vector();
+
+ /** Factory method for creating nested 'message's. */
+ public Message createMessage() {
+ Message msg = new Message();
+ messages.add(msg);
+ return msg;
+ }
+
+ /** A nested 'message'. */
+ public class Message {
+ // Bean constructor
+ public Message() {}
+
+ /** Message to print. */
+ String msg;
+ public void setMsg(String msg) { this.msg = msg; }
+ public String getMsg() { return msg; }
+ }
+
+}
+
+
+And it works:
++C:\tmp\anttests\MyFirstTask>ant +Buildfile: build.xml + +compile: + [mkdir] Created dir: C:\tmp\anttests\MyFirstTask\classes + [javac] Compiling 1 source file to C:\tmp\anttests\MyFirstTask\classes + +jar: + [jar] Building jar: C:\tmp\anttests\MyFirstTask\MyTask.jar + +use.init: + +use.without: + +use.message: +[helloworld] attribute-text + +use.nestedText: +[helloworld] nested-text + +use.nestedElement: +[helloworld] +[helloworld] +[helloworld] +[helloworld] +[helloworld] Nested Element 1 +[helloworld] Nested Element 2 + +use: + +BUILD SUCCESSFUL +Total time: 3 seconds +C:\tmp\anttests\MyFirstTask>ant use.fail +Buildfile: build.xml + +compile: + +jar: + +use.init: + +use.fail: + +BUILD FAILED +C:\tmp\anttests\MyFirstTask\build.xml:36: Fail requested. + +Total time: 1 second +C:\tmp\anttests\MyFirstTask> ++Next step: test ... + + + + +
We have written a test already: the use.* tasks in the buildfile. But its +difficult to test that automatically. Common (and in Ant) used is JUnit for +that. For testing tasks Ant provides a baseclass org.apache.tools.ant.BuildFileTest. +This class extends junit.framework.TestCase and can therefore be integrated +into the unit tests. But this class provides some for testing tasks useful methods: +initialize Ant, load a buildfile, execute targets, +expecting BuildExceptions with a specified text, expect a special text +in the output log ...
+ +In Ant it is usual that the testcase has the same name as the task with a prepending +Test, therefore we will create a file HelloWorldTest.java. Because we +have a very small project we can put this file into src directory (Antīs own +testclasses are in /src/testcases/...). Because we have already written our tests +for "hand-test" we can use that for automatic tests, too. But there is one little +problem we have to solve: all test supporting classes are not part of the binary +distribution of Ant. So you can build the special jar file from source distro with +target "test-jar" or you can download a nightly build from + +http://gump.covalent.net/jars/latest/ant/ant-testutil.jar [5].
+ +For executing the test and creating a report we need the optional tasks <junit> +and <junitreport>. So we add to the buildfile: +
+...
+<project name="MyTask" basedir="." default="test">
+...
+ <property name="ant.test.lib" value="ant-testutil.jar"/>
+ <property name="report.dir" value="report"/>
+ <property name="junit.out.dir.xml" value="${report.dir}/junit/xml"/>
+ <property name="junit.out.dir.html" value="${report.dir}/junit/html"/>
+
+ <path id="classpath.run">
+ <path path="${java.class.path}"/>
+ <path location="${ant.project.name}.jar"/>
+ </path>
+
+ <path id="classpath.test">
+ <path refid="classpath.run"/>
+ <path location="${ant.test.lib}"/>
+ </path>
+
+ <target name="clean" description="Delete all generated files">
+ <delete failonerror="false" includeEmptyDirs="true">
+ <fileset dir="." includes="${ant.project.name}.jar"/>
+ <fileset dir="${classes.dir}"/>
+ <fileset dir="${report.dir}"/>
+ </delete>
+ </target>
+
+ <target name="compile" description="Compiles the Task">
+ <mkdir dir="${classes.dir}"/>
+ <javac srcdir="${src.dir}" destdir="${classes.dir}" classpath="${ant.test.lib}"/>
+ </target>
+...
+ <target name="junit" description="Runs the unit tests" depends="jar">
+ <delete dir="${junit.out.dir.xml}" />
+ <mkdir dir="${junit.out.dir.xml}" />
+ <junit printsummary="yes" haltonfailure="no">
+ <classpath refid="classpath.test"/>
+ <formatter type="xml"/>
+ <batchtest fork="yes" todir="${junit.out.dir.xml}">
+ <fileset dir="${src.dir}" includes="**/*Test.java"/>
+ </batchtest>
+ </junit>
+ </target>
+
+ <target name="junitreport" description="Create a report for the rest result">
+ <mkdir dir="${junit.out.dir.html}" />
+ <junitreport todir="${junit.out.dir.html}">
+ <fileset dir="${junit.out.dir.xml}">
+ <include name="*.xml"/>
+ </fileset>
+ <report format="frames" todir="${junit.out.dir.html}"/>
+ </junitreport>
+ </target>
+
+ <target name="test"
+ depends="junit,junitreport"
+ description="Runs unit tests and creates a report"
+ />
+...
+
+
+Back to the src/HelloWorldTest.java. We create a class extending +BuildFileTest with String-constructor (JUnit-standard), a setUp() +method initializing Ant and for each testcase (targets use.*) a testXX() +method invoking that target. +
+import org.apache.tools.ant.BuildFileTest;
+
+public class HelloWorldTest extends BuildFileTest {
+
+ public HelloWorldTest(String s) {
+ super(s);
+ }
+
+ public void setUp() {
+ // initialize Ant
+ configureProject("build.xml");
+ }
+
+ public void testWithout() {
+ executeTarget("use.without");
+ assertEquals("Message was logged but should not.", getLog(), "");
+ }
+
+ public void testMessage() {
+ // execute target 'use.nestedText' and expect a message
+ // 'attribute-text' in the log
+ expectLog("use.message", "attribute-text");
+ }
+
+ public void testFail() {
+ // execute target 'use.fail' and expect a BuildException
+ // with text 'Fail requested.'
+ expectBuildException("use.fail", "Fail requested.");
+ }
+
+ public void testNestedText() {
+ expectLog("use.nestedText", "nested-text");
+ }
+
+ public void testNestedElement() {
+ executeTarget("use.nestedElement");
+ assertLogContaining("Nested Element 1");
+ assertLogContaining("Nested Element 2");
+ }
+}
+
+
+When starting ant weīll get a short message to STDOUT and +a nice HTML-report. +
+C:\tmp\anttests\MyFirstTask>ant +Buildfile: build.xml + +compile: + [mkdir] Created dir: C:\tmp\anttests\MyFirstTask\classes + [javac] Compiling 2 source files to C:\tmp\anttests\MyFirstTask\classes + +jar: + [jar] Building jar: C:\tmp\anttests\MyFirstTask\MyTask.jar + +junit: + [mkdir] Created dir: C:\tmp\anttests\MyFirstTask\report\junit\xml + [junit] Running HelloWorldTest + [junit] Tests run: 5, Failures: 0, Errors: 0, Time elapsed: 2,334 sec + + + +junitreport: + [mkdir] Created dir: C:\tmp\anttests\MyFirstTask\report\junit\html +[junitreport] Using Xalan version: Xalan Java 2.4.1 +[junitreport] Transform time: 661ms + +test: + +BUILD SUCCESSFUL +Total time: 7 seconds +C:\tmp\anttests\MyFirstTask> ++ + + +
This tutorial and its resources are available via +BugZilla [6]. +The ZIP provided there contains