Excluding classes in Maven Checkstyle plugin reports

I have a Maven 2 project and I want to configure my Checkstyle report plugin so that only some of my classes are analysed. I have found the maven.checkstyle.excludes property, but despite passing this as a command line parameter (using -D=maven.checkstyle.excludes=...) I can't get it to work. I can't find anything on the Plugin documentation page. Ideally I want to be able to set this in the <configuration> section of my POM.

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.

If this question is about Maven 2, then the property is excludes and takes a comma-separated list of Ant patterns. So either pass this on the command line:

-Dexcludes=**/generated/**/*

Or set it up in the plugin configuration:

<plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-checkstyle-plugin</artifactId>
   <configuration>
       <excludes>**/generated/**/*</excludes>
   </configuration>
</plugin>

Another option would be to use a suppression filter.

For example you could use the SuppressionCommentFilter to suppress audit events between a comment containing CHECKSTYLE:OFF and a comment containing CHECKSTYLE:ON (then just add these comments to the classes or parts of the code you don't want to check).

Additionally, if you want to exclude multiple independent folders, you can add multiple independent paths comma separated like this

<excludes>org/log4j/*,com/acme/**/*,com/companyb/*</excludes>

The answers above didn't work for me as I'm running code generation in maven which also adds the target/generated as a source dir.

The following solution works: You have to use an explicit checkstyle-suppressions.xml config file and activate it from your configuration:

<plugins>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-checkstyle-plugin</artifactId>
    <version>3.1.1</version>
    <configuration>
      <configLocation>checkstyle.xml</configLocation>
      <suppressionsLocation>checkstyle-suppressions.xml</suppressionsLocation>
   [...]

The suppressions file for excluding the target folder looks like this:

<?xml version="1.0"?>
<!DOCTYPE suppressions PUBLIC
  "-//Checkstyle//DTD SuppressionFilter Configuration 1.2//EN"
  "https://checkstyle.org/dtds/suppressions_1_2.dtd">

<suppressions>
  <suppress files="[/\\]target[/\\]" checks=".*" />
</suppressions>