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 isn't 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 Ant's 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 Ant's 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, get's 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 - let's 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");
// Task's 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, what's that in execute()? Throw a BuildException? Yes, that's 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 it's necessary because the log() method can't 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>
That's 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
Project's 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.
* Print a message or let the build fail.
* @author Jan Matèrne
* @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 (Ant's 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 we'll 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>
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