How to execute an Ant task only when source files have been modified?

Question

There must be an easy way to do this. I build a Flex app using ant that depends on a SWC library, which works fine except that it rebuilds the library whether it needs to or not. How do I tell ant to only run the task if any of the sources files of the library (*.as, *.mxml) are newer than the SWC?

I've looked at <dependset> but it only seems to delete files, not determine whether a task should be run or not. <depend> seems to expect a one-to-one relationship between the source and target files rather than a one-to-many relationship -- I have many input files and one output file, but no intermediate object files.

Thanks a lot, Alex

Answer 1

You may use the Ant uptodate task to create a property, and execute your other target only if that property is set.

I don't know much about flex, but you probably want something like this:

<?xml version="1.0" encoding="UTF-8"?>
<project name="test" default="compile">

   <target name="checkforchanges">
      <uptodate property="nochanges">
         <srcfiles dir="." includes="**/*.as"/>
         <srcfiles dir="." includes="**/*.mxml"/>
         <mapper to="applicaton.flex"/>
      </uptodate>
   </target>

   <target name="compile" depends="checkforchanges" unless="nochanges">
      ...
   </target>

</project>