To do that you need to use an ant task.

<tasks name="generePropertiesFile">
<!-- ensure that the target directory has been created. -->
<mkdir dir="target/classes/" />
<propertyfile file="target/classes/"
comment="comment in the file.">
<!-- list or key / value pair to be inserted in the generated properties file.  -->
<entry key="key1" value="${basedir}/value1" />
<entry key="key2" value="${basedir}/value2" />

I almost use it on every project because when you try to use maven properties like ${basedir} you won't have problème with the file separator nightmare since this ant task escape properly the '\' caractère.