Maven 2 and Checkstyle

Wednesday, May 23, 2007

I recently wrote an article about integrating Maven 2 with WebLogic Portal and I found working with Maven an interesting experience. One excellent feature of Maven 2 that I am extensively using is the ability to generate a web site for the project automatically. This web site can include a variety of generated reports including project information and documentation, the results of your unit tests, javadoc and more.

One of the available reports in Maven is a Checkstyle report, I wanted to leverage it in order to ensure compliance with the organization's coding standards. If you are not familiar with Checkstyle, it parses your source code and provides a report with regards to how compliant the code is with a given convention. Additional information on Checkstyle can be found at http://checkstyle.sourceforge.net.

Checkstyle ships with a few default conventions including the Sun coding standards, however most organizations customize this and create their own configuration. The question arises though as to how to centralize this configuration so that it does not need to be manually configured when a project build is done.

Fortunately, this issue is easily addressed using the built-in dependency mechanism in Maven. Essentially we simply bundle the Checkstyle xml configuration file into a JAR and then install this into a Maven repository, typically this will be an organization's internal intranet repository. When the project site is built, this configuration is automatically fetched from the repository and applied when needed.

Configuring this is straightforward, first in the project pom.xml we define the dependency on the checkstyle configuration JAR as an extension dependency, this can be done as follows:

<build>
    <extensions>
        <extension>
            <groupId>com.bea.ps</groupId>
            <artifactId>checkstyle-config</artifactId>
            <version>1.0.0</version>
        </extension>
    </extensions>
</build>

Next we reference the configuration file in the Checkstyle plug-in configuration in the reporting section. Note that the Checkstyle plugin will search the URL classpath for the resource before trying the file system, this is why storing the configuration file in a JAR works. The configLocation referenced below is where checks.xml is located on the classpath in the checkstyle-config.jar referenced above.

<reporting>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-checkstyle-plugin</artifactId>
            <configuration>
              <configLocation>config/checks.xml</configLocation>
            </configuration>
        </plugin>
    </plugins>
</reporting>

That should be it, now the configuration can be centrally managed and controlled and projects can get the latest version simply by updating the version of the artifact in the extension section.

Posted by Gerald Nunn at 4:02 PM | Categories: Java | | | Permalink