Using uptodate to speed up builds

antexample2

<target name="check.retrieve.necessary" description="Only retrieve jars with Ivy if necessary">
  <ivy:resolve file="${ivy.file}" transitive="true"/>
  <uptodate property="libs.uptodate">
  <srcfiles dir="." includes="${ivy.file}"/>
  <mapper type="merge" to="{lib.dir}/.done"/>
  </uptodate>
</target>

<target name="resolve" depends="check.retrieve.necessary" description="--> resolve and retrieve dependencies with ivy"
  unless="libs.uptodate">
  <delete includeemptydirs="true" dir="${lib.dir}"/>
  <mkdir dir="${job.lib.dir}"/> <!-- not usually necessary, ivy creates the directory IF there are dependencies -->
  <mkdir dir="${test.lib.dir}"/> 
  <ivy:retrieve pattern="${job.lib.dir}/[artifact]-[revision].[ext]" conf="job" />
  <ivy:retrieve pattern="${test.lib.dir}/[artifact]-[revision].[ext]" conf="test" />
  <touch file="${lib.dir}/.done" />
</target>