Java Linting and Code Quality Tools: Checkstyle, PMD, and SpotBugs

When building Java applications, writing clean, maintainable, and bug-free code is crucial for long-term success. Poor quality code can lead to hard-to-diagnose bugs, security vulnerabilities, and a poor developer experience. Fortunately, Java offers several tools to automate code quality checks and linting.

In this article, we’ll dive deep into Java Linting and Code Quality Tools, focusing on three of the most popular ones:

Checkstyle
PMD
SpotBugs

You'll learn what they are, why they are important, and how you can integrate them into your project to write better Java code.

What is Code Linting and Static Analysis?

Code linting refers to automatically checking your source code for programmatic and stylistic errors. A linter will scan your code without running it, based on predefined rules or configurations.

Static code analysis is the process of analyzing code for potential errors, vulnerabilities, and poor practices before the program is run.

Both aim to:

Catch bugs early
Enforce coding standards
Improve maintainability
Reduce technical debt

Why Use Linting and Code Quality Tools?

Here are some compelling reasons:

Catch bugs before production: Save time and money.
Standardize code style: Enforce uniform coding practices across teams.
Enhance readability: Clean code is easier to understand and modify.
Reduce security risks: Find common vulnerabilities like SQL injection or null pointer dereferences.
Automate code reviews: Free up time for deeper, more meaningful code reviews.

Checkstyle

What is Checkstyle?

Checkstyle is a development tool to help programmers write Java code that adheres to a coding standard. It automates the process of checking Java code for compliance with coding rules.

It focuses more on stylistic issues like formatting, naming conventions, Javadoc comments, and more.

Think of Checkstyle as your strict teacher who ensures your code "looks" neat and consistent.

Features of Checkstyle

Enforces coding standards (e.g., Google's Java Style Guide)
Checks for proper JavaDoc comments
Identifies missing or misordered modifiers
Flags long methods or classes
Highly customizable with XML configuration

How to Use Checkstyle

Using Maven

Add this plugin to your pom.xml:

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-checkstyle-plugin</artifactId>
      <version>3.3.1</version>
      <configuration>
        <configLocation>google_checks.xml</configLocation> <!-- Or your custom rules -->
        <failOnViolation>true</failOnViolation>
      </configuration>
      <executions>
        <execution>
          <phase>validate</phase>
          <goals>
            <goal>check</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

You can then run:

mvn checkstyle:check

PMD

What is PMD?

PMD is a source code analyzer. It finds common programming flaws like:

Unused variables
Empty catch blocks
Unnecessary object creation
Potential bugs like infinite loops

While Checkstyle is about how your code looks, PMD is about what your code is doing wrong logically.

Features of PMD

Identifies code that can be optimized
Detects potential bugs and security flaws
Helps enforce best practices
Supports multiple languages (Java, Apex, JavaScript, etc.)
Offers pre-built and custom rule sets

How to Use PMD

Using Maven

Add PMD to your pom.xml:

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-pmd-plugin</artifactId>
      <version>3.15.0</version>
      <configuration>
        <printFailingErrors>true</printFailingErrors>
      </configuration>
      <executions>
        <execution>
          <phase>verify</phase>
          <goals>
            <goal>check</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

To run:

mvn pmd:check

SpotBugs

What is SpotBugs?

SpotBugs is a static analysis tool that looks for bugs in Java programs. It's the successor of the popular tool FindBugs.

It scans Java bytecode rather than the source code, meaning it can catch some runtime issues that other static analyzers might miss.

Features of SpotBugs

Finds NullPointerExceptions
Detects bad practices like "equals" without "hashCode"
Identifies performance issues
Security flaw detection
Supports plugins like FindSecurityBugs for advanced scanning

How to Use SpotBugs

Using Maven

Add SpotBugs to your pom.xml:

<build>
  <plugins>
    <plugin>
      <groupId>com.github.spotbugs</groupId>
      <artifactId>spotbugs-maven-plugin</artifactId>
      <version>4.7.3.0</version>
      <configuration>
        <effort>Max</effort>
        <threshold>Low</threshold>
      </configuration>
      <executions>
        <execution>
          <phase>verify</phase>
          <goals>
            <goal>check</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

Run it with:

mvn spotbugs:check

Integrating These Tools into Your Build (Maven/Gradle)

Modern Java projects use Maven or Gradle for build management. All three tools (Checkstyle, PMD, SpotBugs) can be integrated easily with both:

Maven Plugins: As shown in examples above.
Gradle Plugins:
- checkstyle
- pmd
- com.github.spotbugs

Example in Gradle:

plugins {
    id 'checkstyle'
    id 'pmd'
    id 'com.github.spotbugs' version '5.0.13'
}

checkstyle {
    toolVersion = '10.3.4'
}

pmd {
    toolVersion = '6.55.0'
}

spotbugs {
    toolVersion = '4.7.3'
}

Run:

./gradlew check

Best Practices for Code Quality

Shift Left: Catch issues early in the development cycle.
Use All Three Tools Together: They complement each other.
Automate in CI/CD Pipelines: Fail the build if serious violations are found.
Custom Rule Sets: Customize rules to match your project's standards.
Review Regularly: Periodically update and fine-tune the rules.
Focus on Readability: Write code for humans first, machines second.
Educate Developers: Train your team on how to interpret and fix tool warnings.

Conclusion

Writing high-quality Java code is not just about making things work — it’s about making them maintainable, readable, efficient, and secure. Tools like Checkstyle, PMD, and SpotBugs are essential companions for any serious Java developer.

By integrating these tools into your development process, you automate quality assurance, enforce standards, and drastically reduce bugs before they reach production.

Start small — pick one tool, configure it for your project, and gradually expand. Your future self (and your teammates) will thank you!