Generate Javadoc without duplicate execution of phase generate-sources.

• The standard goals javadoc and test-javadoc invoke separate lifecyles generate-sources and generate-test-sources.
• In a CI environment you now might execute something like mvn clean deploy site site-deploy.
• During site build the standard reports will trigger generate-sources or generate-test-sources again, depending on your build this may take some time, because stuff like enforcer or generating stubs from a WDSL will be invoked again, which may lead to longer build times.
• See MJAVADOC-369 as well.
• As of version 2.10 two new reports are defined, javadoc-no-fork and test-javadoc-no-fork which will not trigger above phases a second time.
• Configure this in your reporting section as follows:

  <project>
   ...
   <reporting>
   <excludeDefaults>true</excludeDefaults>
   <plugins>
   <plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-javadoc-plugin</artifactId>
   <version>3.12.0</version>
   <reportSets>
   <reportSet>
   <reports>
   <report>javadoc-no-fork</report>
   <report>test-javadoc-no-fork</report>
   </reports>
   </reportSet>
   </reportSets>
   </plugin>
   </plugins>
   </reporting>
   ...
  </project>

  Note: These reports may not be used for aggregate reports. For those, see the example of generating aggregate Javadocs without execution of phase compile.