Here is a correct implementation, using the maven-dependency-plugin properties goal, which can be used anywhere in a pom:
<?xml version="1.0" encoding="UTF-8"?>
<project>
<modelVersion>4.0.0</modelVersion>
<groupId>com.stackoverflow</groupId>
<artifactId>q2359872</artifactId>
<version>2.0-SNAPSHOT</version>
<name>q2359872</name>
<properties>
<!-- Must be listed in the dependencies section otherwise it will be null. -->
<my.lib>${org.jmockit:jmockit:jar}</my.lib>
</properties>
<dependencies>
<dependency>
<groupId>org.jmockit</groupId>
<artifactId>jmockit</artifactId>
<version>1.11</version>
</dependency>
</dependencies>
<build>
<defaultGoal>generate-sources</defaultGoal>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.3</version>
<executions>
<execution>
<goals>
<goal>properties</goal>
</goals>
</execution>
</executions>
</plugin>
<!-- Example usage: -->
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.2</version>
<executions>
<execution>
<goals>
<goal>exec</goal>
</goals>
<phase>generate-sources</phase>
</execution>
</executions>
<configuration>
<executable>echo</executable>
<arguments>
<argument>path to jar=</argument>
<argument>${org.jmockit:jmockit:jar}</argument>
<argument>my.lib=</argument>
<argument>${my.lib}</argument>
</arguments>
</configuration>
</plugin>
<!-- end of Example usage -->
</plugins>
</build>
</project>
And the output is...
jpyeron@black /projects/wkspc/tmp/foo
$ /cygdrive/c/programs.x86_64/apache-software-foundation/apache-maven-3.1.1/bin/mvn
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building q2359872 2.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-dependency-plugin:2.3:properties (default) @ q2359872 ---
[INFO]
[INFO] --- exec-maven-plugin:1.2:exec (default) @ q2359872 ---
path to jar= C:Documents and Settingsjpyeron.m2
epositoryorgjmockitjmockit1.11jmockit-1.11.jar my.lib= C:Documents and Settingsjpyeron.m2
epositoryorgjmockitjmockit1.11jmockit-1.11.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.032s
[INFO] Finished at: Wed Sep 17 12:07:18 EDT 2014
[INFO] Final Memory: 10M/153M
[INFO] ------------------------------------------------------------------------
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