example-ant-single-jar.xml

<?xml version="1.0"?>
<project name="validate-cli" default="install">

    <property file="../parent-build.properties"/>
    <property file="build.properties"/>

    <property name="src.dir" location="src/main/java"/>

    <property name="build.dir" location="target"/>
    <property name="build.lib.dir" location="${build.dir}/lib"/>
    <property name="test.report.dir" location="${build.dir}/report"/>

    <path id="src.classpath">
        <fileset dir="${lib.dir}/required">
            <include name="**/*.jar"/>
        </fileset>
        <file file="${jar.validate-lib}"/>
    </path>

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

    <target name="create-folders">
        <mkdir dir="${build.dir}"/>
        <mkdir dir="${build.lib.dir}"/>
    </target>

    <target name="compile" depends="clean, create-folders">
        <javac source="${java.jdk.version}" target="${java.jdk.version}" debug="${build.debug}" srcdir="${src.dir}"
               destdir="${build.dir}" encoding="${encoding.default}" includeantruntime="${ant.includeantruntime}">
            <classpath>
                <path refid="src.classpath"/>
            </classpath>
        </javac>
        <copy todir="${build.lib.dir}" flatten="true">
            <path refid="src.classpath"/>
        </copy>
        <pathconvert property="mf.classpath" pathsep=" ">
            <path refid="src.classpath" />
            <flattenmapper />
        </pathconvert>
        <tstamp/>
        <manifest file="MANIFEST.MF">
            <attribute name="Code-Url" value="${application.url}"/>
            <attribute name="Built-By" value="${user.name}"/>
            <attribute name="Built-Date" value="${TODAY}"/>
            <attribute name="Built-Version" value="${application.version}"/>
            <attribute name="Main-Class" value="no.difi.vefa.cli.App"/>
            <attribute name="Class-Path" value="${mf.classpath}" />
        </manifest>
        <jar destfile="${build.dir}/${out.jar}" basedir="${build.dir}" includes="**/*.*" manifest="MANIFEST.MF"/>
    </target>

    <target name="install" depends="compile">
        <description>Install the build</description>
    </target>

</project>

Important! The libaries must be prefixed with the correct folder :-)