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Ant Properties, Datatypes & References

COMP285 Lectures

Datatypes

The following datatypes are available in Ant:

  • Paths - An ordered list of files and directories.
    • Classpath is a variant of this.
  • Filesets - A collection of files rooted from a specified directory.
  • Patternsets - A collection of file matching patterns.
  • Filtersets

Properties

This is a way of defining variables that you can use in your build:

  • They are defined as key-value pairs.
  • They are immutable.

Built-in Properties

You can see a list of system properties such as:

%{os.name}

at the following link: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/ System.html#getProperties().

Storing Locations in Properties

To allow for processing of file-paths you should use the location attribute instead of value:

<property name="dir" location="somedir"/>

This will allow prepending of the basedir and formatting the path for the OS.

Setting Properties

Setting Properties via Task

You can set, and use, properties by using the <property> task like so:

<property name="build.debug" value="on"/>
<javac srcdir="src" debug="${build.debug}"/>

Setting Properties via Command-Line

You can set properties on the command line using the -D<property>=<value> syntax:

$ ant -Dbuild.debug=off -f build.xml

You can also include a property file:

$ ant -propertyfile build.properties

-D flags take precedence over the property file.

Setting Properties from File

You can create a file, such as build.properties to hold your values in an ini style:

build.debug=off
build.dir=build
output.dir=${build.dir}/output

This properties file can then be loaded using the following task:

<property file="build.properties"/>

Setting Properties from Environment Variables

We can store all the environment variables in a property called env like so:

<property environment="env"/>

We can then access them using their name:

<echo message="The PATH is: ${env.PATH}">

Global Properties

There is no concept of scope for properties but if you want them to be available for multiple targets, you should assign them under <project>:

<project name="test">
	<property name="..." value="..."/>
	<target>
		...
	</target>
</project>

This ensures they are executed before the target.

<available>

We can set a property when a resource is available by using this task:

<property name="project.jar" value="./dist/project.jar"/>

<available file="${project.jar}"
	type="file"
	property="project.jar.present"
/>
<echo message="file ${project.jar} is present=${project.jar.present}"/>

This method can work on:

  • Classes in a Classpath
  • Files & Directories
  • Resource Files (.jar files)

The man page is here: https://ant.apache.org/manual/Tasks/available.html.

Conditional Execution

We can use if and unless to execute tasks depending on a property:

<target name="build-module-A" if="module-A-present"/>
<target name="build-module-B" unless="module-A-present"/>
  • Unset properties are falsy.
  • Everything else is truthy.

References

We can save several attribute definitions using a reference:

<path id="compile.classpath">
	<pathelement location="${lucene.jar}"/>
	<pathelement location="${tidy.jar}"/>
</path>

We can then use these pathelements else where by using refid:

<path id="test.classpath">
	<path refid="compile.classpath"/>
	<pathelement location="${junit.jar}"/>
	<pathelement location="${build.dir}/classes"/>
	<pathelement location="${build.dir}/test"/>
</path>

We can also use datatypes other than path.

If you are going to reuse this datatype then you can name it using a property:

<project name="ref-classpath" basedir="dist">
	<path id="test.classpath">
		<pathelement location="build/classes"/>
		<pathelement location="src"/>
	</path>
	<property name="path" refid="test.classpath"/>
	<echo>path is ${path}</echo>
</project>

This makes a standalone datatype.

This will produce an output like so:

$ ant
Buildfile: /home/ben/ref-classpath/build.xml
	[echo] path is /home/ben/ref-classpath/dist/build/classes:/home/ben/ref-classpath/dist/src

BUILD SUCCESSFUL
Total time: 0 seconds

Notice how this takes into account the basedir.