Excluding classes in Maven Checkstyle plugin reports

If, like me, you arrived here searching for a way to exclude generated sources from checkstyle, do this:

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-checkstyle-plugin</artifactId>
  <version>2.15</version>
  <configuration>
    <sourceDirectory>${project.build.sourceDirectory}</sourceDirectory>
  </configuration>
</plugin>

By default, the checkstyle:checkstyle goal of the checkstyle plugin uses ${project.compileSourceRoots}, which apparently includes generated source directories.

If you change it to ${project.build.sourceDirectory}, it will use only the source directory, not any generated source directories.

Note that while <sourceDirectory> is deprecated, the alternative, <sourceDirectories>, does not appear to work.

Edit: In comments, @Cyrusmith, @Ben, and @Olivier Callioux report that as of 2017, <sourceDirectories> works; I cannot confirm.