In the test I want to prepare javadocs only for the class org.apache.project.IncludeClass. All other classes located in packages io and org.apache.internal should be skipped.

Configuration I use is the following:

          <subpackages>org.apache</subpackages>
          <excludePackageNames>org.apache.internal:org.apache.internal.*</excludePackageNames>

It works well for java8, but for java11 (actually since java9) it doesn't exclude the class org.apache.internal.subpackage.subsubpackage.ExcludeInternalSubSubClass.

I tried comment the "subpackages" setting and now it excludes the ExcludeInternalSubSubClass. This behavior is not obvious for me, I expect that exclusion rules should not depend on the "subpackages" setting.

I debug it and found:

1. Behavior for exclusion is actually depends on whether the "subpackages" setting is specified or not - there are different patterns for exclusion used, see patterns in JavadocUtil#getExcludedPackages and JavadocUtil#getIncludedFiles.
2. If the "subpackages" setting is used, the plugin prepares equal options for the javadoc util for both java versions. But actually the output for the javadoc util differs. I tried the same command
   javadoc -sourcepath ./src/main/java -subpackages org.apache -exclude org.apache.internal -d javadoc
   for both java version and it returns different result. I'm not sure is it expected behavior, but I'd expect the javadoc plugin will adjust for different java versions.