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Multimodule Configuration

If you have a multimodule project with many modules and you want to share the PMD ruleset configuration, so that each module uses the same PMD rules, this is possible, but requires a little setup.

The setup is very similar to the one described for Checkstyle, see Multimodule Configuration for Checkstyle.

This example will use the same mysterious project called whizbang. This is what the structure of that project looks like:

whizbang
|-- pom.xml
|-- core
|   `-- pom.xml
|-- gui
|   `-- pom.xml
|-- jmx
|   `-- pom.xml
`-- src

Create a subproject for the PMD rulesets

We'll start by adding another sub project that will house our common configuration for PMD. Let's call it build-tools. In it we put the resources that we want to share between our whizbang modules. In this example, we will add our custom PMD ruleset to be used by the PMD Plugin. The same subproject can be used to house shared configurations for Checkstyle.

whizbang
|-- pom.xml
|-- build-tools
|   |-- src
|   |   `-- main
|   |       `-- resources
|   |           `-- whizbang
|   |               `-- pmd-ruleset.xml
|   `-- pom.xml
|-- core
|-- gui
|-- jmx
`-- src

Tip: put the resources into a subdirectory that you can ensure will be unique and not conflict with anyone else.

The pom.xml file for build-tools should look like this:

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.example.whizbang</groupId>
  <artifactId>build-tools</artifactId>
  <version>1.0</version>
  <name>Build Tools</name>
</project>

A sample pmd-ruleset.xml could look like this:

<?xml version="1.0"?>
<ruleset name="whizbang PMD ruleset"
    xmlns="http://pmd.sourceforge.net/ruleset/2.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://pmd.sourceforge.net/ruleset/2.0.0 http://pmd.sourceforge.net/ruleset_2_0_0.xsd">

    <description>
        This ruleset defines the PMD rules for project "whizbang".
    </description>

    <rule ref="category/java/bestpractices.xml/AvoidUsingHardCodedIP" />
    <rule ref="category/java/bestpractices.xml/CheckResultSet" />
    <rule ref="category/java/bestpractices.xml/UnusedImports" />
    <rule ref="category/java/bestpractices.xml/UnusedFormalParameter" />
    <rule ref="category/java/bestpractices.xml/UnusedLocalVariable" />
    <rule ref="category/java/bestpractices.xml/UnusedPrivateField" />
    <rule ref="category/java/bestpractices.xml/UnusedPrivateMethod" />

    <rule ref="category/java/codestyle.xml/DontImportJavaLang" />
    <rule ref="category/java/codestyle.xml/DuplicateImports" />

    <rule ref="category/java/errorprone.xml/AvoidBranchingStatementAsLastInLoop" />
    <rule ref="category/java/errorprone.xml/AvoidDecimalLiteralsInBigDecimalConstructor" />
    <rule ref="category/java/errorprone.xml/AvoidMultipleUnaryOperators" />
    <rule ref="category/java/errorprone.xml/AvoidUsingOctalValues" />
    <rule ref="category/java/errorprone.xml/BrokenNullCheck" />

    <!-- many more rules are available at https://pmd.github.io/pmd-6.21.0/pmd_rules_java.html -->
</ruleset>

The ruleset references some built-in rules. For more information about rulesets, see Making Rulesets and Using Rule Sets.

Configure the other projects to use it

Now we can include the PMD configuration in the top level pom.xml.

Note: You have to specify a plugin dependency on build-tools in the <build> element of your pom.xml. It will not work inside the <reporting> element, because <reporting> does not support plugin dependencies. The rest of the configuration is done in the normal way in the <reporting> element.

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.example.whizbang</groupId>
  <artifactId>whizbang-parent</artifactId>
  <version>1.0</version>
  <packaging>pom</packaging>
  <name>WhizBang Parent</name>
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-pmd-plugin</artifactId>
        <version>3.13.0</version>
        <configuration>
          <rulesets>
            <ruleset>whizbang/pmd-ruleset.xml</ruleset>
          </rulesets>
          <printFailingErrors>true</printFailingErrors>
        </configuration>
        <executions>
          <execution>
            <goals>
              <goal>check</goal>
            </goals>
          </execution>
        </executions>
        <dependencies>
          <dependency>
            <groupId>com.example.whizbang</groupId>
            <artifactId>build-tools</artifactId>
            <version>1.0</version>
          </dependency>
        </dependencies>
      </plugin>
    </plugins>
  </build>
  <reporting>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-pmd-plugin</artifactId>
        <version>3.13.0</version>
        <configuration>
          <rulesets>
            <ruleset>whizbang/pmd-ruleset.xml</ruleset>
          </rulesets>
        </configuration>
      </plugin>
    </plugins>
  </reporting>
  <modules>
    <module>build-tools</module>
    <module>core</module>
    <module>jmx</module>
    <module>gui</module>
  </modules>
</project>

Once you are done with that, ensure that you do not include the Maven PMD Plugin in your sub modules, as their definition and configuration, will override the top level parent pom's definition.

Based on the PMD Plugin configuration above, the values of rulesets will be resolved from the classpath. The build-tools JAR was included in the classpath when it was declared as a dependency to the plugin.

Lastly, kick off a build of the site.

mvn site

Or run the check goal of the PMD plugin via verify:

mvn verify

Every sub project will now use the same PMD setup and configuration.