Calling Ant targets dynamically in Jenkins - ant

Question

Is there a way to call Ant targets in 'Invoke Ant' build step dynamically? Say you have a build.xml with:
<target name="1" description="1">
<exec executable="${RES_DIR}/1.sh" failonerror="true">
</exec>
</target>
<target name="2" description="2">
<exec executable="${RES_DIR}/2.sh" failonerror="true">
</exec>
</target>
<target name="3" description="3">
<exec executable="${RES_DIR}/3.sh" failonerror="true">
</exec>
</target>
And want your Jenkins builds to all use this same build.xml, but to be able to call certain targets for each build. I don't want to hardcode these targets everytime a project needs to be created because I want it to be done automatically. Is this possible or do you have to create a project beforehand and manually set your Ant targets?

Answer 1

A simple trick can be to use the if attribute on targets.
For instance:
<target name="run" depends="1,2,3" />
<target name="1" description="1" if="run1">
<exec executable="${RES_DIR}/1.sh" failonerror="true">
</exec>
</target>
<target name="2" description="2" if="run2">
<exec executable="${RES_DIR}/2.sh" failonerror="true">
</exec>
</target>
<target name="3" description="3" if="run3">
<exec executable="${RES_DIR}/3.sh" failonerror="true">
</exec>
</target>
That way, you call the target run and set the property runX to an arbitrary value (true is generally a good choice). Only the target X will actually run.

Answer 2

That would probably work OK but it is a bit of an inconvenient to change your build just to satisfy a Jenkins build interface requirement.
The way I usually do it is to set a build parameter say a 'choice' and give the user the possibility to choose which target they want to invoke from that drop down list.
Say that choice parameter is called target then all you need to do in the 'invoke ant' build section is to refer to %target% and Jenkins will make the substitution for you.
Whether you go with a 'choice' or other types of build parameters (e.g. text) would depend on your specific needs.