if ant else

ANT-tidbits.
Here is what I think is the best way to perform one or the other targets in an ant file depending on if a property is set or not.
Let us pretend that if the mainclass property has a value we want to create an executable JAR-file, if not set we will create a plain JAR-file.

<!-- =================================================================
 Create a jar-file of the projects classes
================================================================== -->
<target
 name="jar"
 depends="plain-jar, executable-jar"
 description="--> Create a JAR-file of the project classes."
/>

<target name="executable-jar" if="mainclass">
...
</target>
 
<target name="plain-jar" unless="mainclass">
...
</target>

It is dead simple but still, I've seen a lot of strange antcall with conditions and stuff in the wild to acheive the same thing.

Another little smippet that took a while to get right is to create a class-path in the MANIFEST.MF based on an ANT-path.
This is the best way I have found so far, the silly thing is that it is different if building on windows or on a real operating system.

<pathconvert dirsep="/" pathsep=" " property="manifest-classpath" refid="build.classpath">
 <!--
  The regexp when building on unix is:
  from="/([^/]*.jar)\z"
 -->
 <mapper>
  <mapper 
     type="regexp"
     from="\\([^\\]*.jar)\z" to="lib/\1"
  />
 </mapper>
</pathconvert>

This will set the manifest-classpath property with a value that is suitable for writing in the Manfest attribute Class-Path. In this example it will prefix all path-entries with a lib/ but you can take it from here yourselves :-)

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