how to customer ant task

1, implement Task.
2,<taskdef name="codegen"
classname="com.expedia.e3.platform.messaging.codegen.CodeGenTask"
classpathref="codegen.classpath"
description="Load the CodeGen task and make it available."
loaderref="codegen"/>

<typedef name="rootelementset" classname="com.expedia.e3.platform.messaging.codegen.RootElementSet"
loaderref="codegen" classpathref="codegen.classpath" />


<target name="generate-types" depends="resolve-xsd"
description="generate Java classes for common types, based on the input xsd files">
<codegen outputdir="${codegen.output.root}" sourcefile="${output.lib}/${ant.project.name}-${output.revision}.xsd">
<rootelementset refid="rootelements" />
</codegen>
</target>