build.xml

<?xml version="1.0" encoding="UTF-8"?>
<project name="library" default="package">
    <property name="jarname" location="./bin/${ant.project.name}.jar" />
    <property name="src" location="./src" />
    <property name="bin" location="./bin" />

    <target name="clean">
        <delete dir="${bin}" />
    </target>

    <target name="compile">
        <delete dir="${bin}/*" />
        <javac srcdir="${src}" destdir="${bin}" />
    </target>

    <target name="package" depends="compile">
        <delete file="${jarname}" />
        <jar jarfile="${jarname}">
            <fileset dir="${bin}" />
        </jar>
    </target>
</project>