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>3.1.1</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.