This example pom.xml demonstrates what you need in order to have maven generate a HAR file using maven-har-plugin and execute the regular JAR pacakging.
<project>
...
<build>
...
<plugins>
...
<plugin>
<groupId>net.sf.maven-har</groupId>
<artifactId>maven-har-plugin</artifactId>
<version>1.0</version>
<extensions>true</extensions>
</plugin>
...
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<executions>
<execution>
<goals>
<goal>jar</goal>
</goals>
<phase>package</phase>
</execution>
</executions>
<configuration>
<classifier>jar</classifier>
</configuration>
</plugin>
...
</plugins>
...
</build>
...
<packaging>har</packaging>
...
</project>