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>2.7</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>2.7</version>
<configuration>
<configLocation>checkstyle.xml</configLocation>
<propertesLocation>${basedir}/checkstyle.properties</propertiesLocation>
</configuration>
</plugin>
</plugins>
</reporting>
...
</project>