Why cannot Ant taskdef cannot load a resource outside ./net - ant

Question

When declaring external ant tasks using taskdef, for instance ant-contrib, the proposed setup is to use the followin taskdef:
<taskdef resource="net/sf/antcontrib/antcontrib.properties">
<classpath>
<pathelement location="lib/ant-contrib/ant-contrib-1.0b3.jar"/>
</classpath>
</taskdef>
This works when antcontrib.properties is located in net/sf/antcontrib relative to the build.xml file.
But when I put it in lib/net/sf/antcontrib and changes the taskdef into
<taskdef resource="lib/net/sf/antcontrib/antcontrib.properties">
<classpath>
<pathelement location="lib/ant-contrib/ant-contrib-1.0b3.jar"/>
</classpath>
</taskdef>
Ant is not able to find the properties file, it gives the error
[taskdef] Could not load definitions from resource
lib/net/sf/antcontrib/antcontrib.properties. It could not be found.
It seems like ant treats the lib directory separately and fails to load a taskdef resource from there.

Answer 1

As Alex said, you shouldn't need to unzip the jar. The <taskdef> can load antcontrib.properties directly out of the jar.
The error you got is because you changed the resource path, but the path to the file inside the compressed jar/zip is still the same. The taskdef isn't paying attention to the properties file you moved because the <classpath> you provided to <taskdef> tells it to only look in the jar.

Answer 2

Use antlib.xml resource:
Here is the taskdef definition that I use:
<property name="ant-contrib.jar" location="..."/>
<taskdef
resource="net/sf/antcontrib/antlib.xml"
uri="http://ant-contrib.sourceforge.net"
>
<classpath>
<pathelement location="${ant-contrib.jar}"/>
</classpath>
</taskdef>
You do not need to extract anything from the jar file. Also, uri attribute is optional if you do not want to use namespaces with antcontrib tasks.

Answer 3

To handle classpath for tasks definitions, I use a classpath ref in Ant, it's way easier. You can link either a directory containing classes, either a directory containing many .jar, either (of course) a single .jar.
For example :
<!-- Properties -->
<property name="lib" value="lib/" />
<property name="classes" value="bin/" />
<!-- Classpath definition -->
<path id="runtime-classpath" >
<pathelement location="${bin}" />
<fileset dir="${lib}">
<include name="*.jar"/>
</fileset>
</path>
<!-- Taskdefs definitions -->
<taskdef name="myTask" classname="org.stackoverflow.tasks.MyTask" classpathref="runtime-classpath" />
<!-- Tasks -->
<target name="test" description="Test Action">
<myTask parameter1="value" />
</target>