Prior to 2.8.1 version, you can some additionnal dependencies to the javadoc classpath
For instance, with the following configuration:
<project>
...
<reporting> (or <build>)
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-javadoc-plugin</artifactId>
<version>2.9.1</version>
<configuration>
...
<additionnalDependencies>
<additionnalDependency>
<groupId>geronimo-spec</groupId>
<artifactId>geronimo-spec-jta</artifactId>
<version>1.0.1B-rc4</version>
</additionnalDependency>
</additionnalDependencies>
...
</configuration>
</plugin>
</plugins>
...
</reporting> (or </build>)
...
</project>