build.xml

<project name="roadef" basedir="." default="main">
    <property name="src.dir"      value="src"/>
    <property name="build.dir"    value="build"/>
    <property name="classes.dir"  value="${build.dir}/classes"/>
    <property name="jar.dir"      value="${build.dir}/jar"/>
    <property name="main-class"   value="put.roadef.Main"/>
    <property name="lib.dir"      value= "lib"/>

    <path id="classpath">
        <fileset dir="${lib.dir}" includes="**/*.jar"/>
    </path>

    <!--I must mkdir here; otherwise manifestclasspath fails -->
    <mkdir dir="${jar.dir}"/>
    <!--This is magic-->
    <manifestclasspath property="jar.classpath" jarfile="${jar.dir}/${ant.project.name}.jar">
        <classpath refid="classpath"/>
    </manifestclasspath>

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

    <target name="compile">
        <mkdir dir="${classes.dir}"/>
        <javac srcdir="${src.dir}" destdir="${classes.dir}" classpathref="classpath" debug="on" debuglevel="vars,lines,source"/>
    </target>

    <target name="jar" depends="compile">
        <mkdir dir="${jar.dir}"/>
        <jar destfile="${jar.dir}/${ant.project.name}.jar" basedir="${classes.dir}">
            <zipgroupfileset dir="${lib.dir}" includes="*.jar"/>
            <manifest>
                <attribute name="Main-Class" value="${main-class}"/>
                <attribute name="Class-Path" value="${jar.classpath}"/>
            </manifest>
        </jar>
    </target>

    <target name="run" depends="jar">
        <java jar="${jar.dir}/${ant.project.name}.jar" fork="true"/>
        <classpath>
            <path refid="classpath"/>
            <path location="${jar.dir}/${ant.project.name}.jar"/>
        </classpath>
    </target>

    <target name="main" depends="clean,jar"/>
</project>