If you need to generate a txt with project version / timestamp in project’s root you can use an ant build like this.
<plugins>
...
<plugin>
<artifactId>maven-antrun-plugin</artifactId>
<version>1.8</version>
<executions>
<execution>
<phase>prepare-package</phase>
<configuration>
<tasks>
<tstamp>
<format property="now" pattern="yyyy-MM-dd hh:mm:ss" locale="it" />
</tstamp>
<echo file="<path>/version.txt" append="false">
Project Version : ${project.version} ${line.separator}Build @ ${now}
</echo>
</tasks>
</configuration>
<goals>
<goal>run</goal>
</goals>
</execution>
</executions>
</plugin>
...
</plugins>