Wednesday, November 18, 2020

Add PMD support to Eclipse, Maven, and Jenkins

PMD is a static code analyzer that checks your source for problematic code constructs, design patterns, and code style.

The code smells reported on grown projects might be huge at first, but PMD allows to customize its rules and to adapt them to your needs.

Step 1: Add PMD support to Eclipse

I am using eclipse-pmd which can be installed from the Eclipse Marketplace.

Step 2: Define a ruleset

PMD needs a ruleset to run against. It is stored as an xml file and can be global, workspace specific or project specific. The choice is up to you. For eclipse projects I typically have a "releng" project to host all my configuration files.

A default ruleset looks like this:

<?xml version="1.0"?>
<ruleset name="Custom Rules"

	<description>custom ruleset</description>

	<rule ref="category/java/bestpractices.xml" />
	<rule ref="category/java/codestyle.xml" />
	<rule ref="category/java/design.xml" />
	<rule ref="category/java/documentation.xml" />
	<rule ref="category/java/errorprone.xml" />
	<rule ref="category/java/multithreading.xml" />
	<rule ref="category/java/performance.xml" />
	<rule ref="category/java/security.xml" />

Store your ruleset somewhere in your workspace or on your file system.

Step 3: Enable PMD on project level

Right click on a project in your Eclipse workspace and select Properties. In PMD section check Enable PMD for this project and Add... the ruleset file stored before. The Name is not important and can be freely chosen.

Your rules are live now and PMD should immediately start to add warnings to your code and the Problems view.

Step 4: Refine your rules

The default ruleset might report some issues you do want to treat differently in your project. Therefore you may change rules by setting parameters or disable unwanted rules at all. To alter a rule, you first have to find it in the list of available rules. For disabling you just need to add an exclude node to your rule settings file, eg:

	<rule ref="category/java/bestpractices.xml">
		<!-- logger takes care of guarding -->
		<exclude name="GuardLogStatement" />

Configuring a rule can be done like this:

	<rule ref="category/java/codestyle.xml/ClassNamingConventions">
			<property name="utilityClassPattern"
				value="[A-Z][a-zA-Z0-9]+" />

A full working ruleset as used by one of my projects can be viewed online.

Whenever you change your ruleset you need to recompile your project to get these rules applied. You may do so by selecting Project/Clean... from the main menu.

Step 5: Maven integration

Integration is done by the maven-pmd-plugin. Just add following section to your pom:

			<!-- enable PMD code analysis -->

Make sure to adapt the path to your ruleset accordingly.

Afterwards run your build using

mvn pmd:pmd pmd:cpd

If you use the maven-site-plugin, you may additionally generate html reports of PMD findings.

Step 6: Jenkins integration

Static reports are nice, but charts over time/commits are even better. In case you use Jenkins you may have a look at the warnings-ng plugin. When you generate yout pmd.xml files via maven, this plugin can pick them up and draw nice reports. In a pipeline build this only needs one line:

recordIssues(tools: [cpd(), pmdParser()])

to get charts like these:

Try out the live chart on the skills project.

Finally the plugin even allows to compare the amount of issues against a baseline. This allows to add  quality gates, eg to fail the build in case your issue count increases. I strongly encourage to enforce such rules. Otherwise warnings are nice but do get ignored by everybody.

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