Using Custom Checkstyle Property Expansion Definitions

Custom property expansion definitions for the Checker can be defined.

Checkstyle uses the property expansion mechanism to allow injection of specific values into a pre-defined Checker configuration. Using property expansion alone is an insufficient means to customize the checks performed by Checkstyle.

Example: checkstyle.xml - only checks the package name in use to ensure that it conforms to the desired scheme, but allows for users of this Checker to specify their own projectname.

<?xml version="1.0" ?>

<!DOCTYPE module PUBLIC
  "-//Puppy Crawl//DTD Check Configuration 1.2//EN"
  "http://www.puppycrawl.com/dtds/configuration_1_2.dtd">

<module name="Checker">
  <module name="TreeWalker">
    <module name="PackageName">
      <property name="format"
         value="com\.example\.$\{projectname\}(\.[a-z][a-zA-Z0-9]+)*$"/>
    </module>
  </module>
</module>

Example: pom.xml - Specifies the projectname property expansion that Checkstyle will use when encountering such a variable in the above Checker configuration.

<project>
  ...
  <reporting>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-checkstyle-plugin</artifactId>
        <version>2.12</version>
        <configuration>
          <configLocation>checkstyle.xml</configLocation>
          <propertyExpansion>projectname=whizbang</propertyExpansion>
        </configuration>
      </plugin>
    </plugins>
  </reporting>
  ...
</project>

The property expansion information can also come from a location using the propertiesLocation parameter as shown below. The propertiesLocation can point to a URL, File or build classpath resource reference.

<project>
  ...
  <reporting>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-checkstyle-plugin</artifactId>
        <version>2.12</version>
        <configuration>
          <configLocation>checkstyle.xml</configLocation>
          <propertesLocation>${basedir}/checkstyle.properties</propertiesLocation>
        </configuration>
      </plugin>
    </plugins>
  </reporting>
  ...
</project>