[Ant]Combine two jars into a single jar

 <target name="combine_jar" description="combine two jars into a single jar">
        <jar destfile="${dest.dir}/combine.jar" >
            <zipgroupfileset dir="${dest.dir}" includes="a.jar"/>
            <zipgroupfileset dir="${dest.dir}" includes="b.jar"/>
        </jar>
 </target>