<target name="jar" description="Create MyPlugin jar file" depends="compile">
    <copy file="${basedir}/plugin.props" todir="{$classes.dir}/my/package" />
    <jar destfile="${build.dir}/MyPlugin.jar">
         <manifest>
         <attribute name="Cytoscape-Plugin"
                    value="my.package.MyPlugin" />
         </manifest>

         <fileset dir="${classes.dir}" />
    </jar>
</target>