build.xml

<?xml version="1.0" encoding="UTF-8"?>
<project name="Composer Targets" >

    <property name="builddir" value="build"/>
    <property name="composer" value="${builddir}/composer.phar"/>

    <target name="php-check">
        <condition property="php" value="php">
            <not>
                <isset property="${php}"/>
            </not>
        </condition>
    </target>

    <target name="prepare">
        <mkdir dir="${builddir}" />
    </target>

    <target name="composer-check" depends="prepare">
        <available file="${composer}" property="composer.present"/>
    </target>

    <target name="composer-download" depends="composer-check" unless="composer.present">
        <property name="composer.noselfupdate" value="true"/>
        <get src="https://getcomposer.org/composer.phar" dest="${composer}"/>
    </target>

    <target name="composer-selfupdate" depends="php-check,composer-download" unless="composer.noselfupdate">
        <exec executable="${php}">
            <arg value="${composer}"/>
            <arg value="self-update"/>
            <arg value="--quiet"/>
        </exec>
    </target>

    <target name="composer" depends="composer-selfupdate" unless="composer.noupdate" description="Run composer update">
        <exec executable="${php}" failonerror="true">
            <arg value="${composer}"/>
            <arg value="update"/>
        </exec>
    </target>

</project>