Spotless in Multi-Module Maven Projects

Spotless in Multi-Module Maven Projects | Generated by AI

Home 2025.10

Spotless in Multi-Module Maven Projects

Spotless is a code formatting plugin available for both Maven and Gradle. Based on your mention of Maven’s -pl (project list) flag, I’ll assume you’re using the Spotless Maven plugin in a multi-module Java project. This allows you to run formatting checks (e.g., via spotless:check) or apply fixes (e.g., via spotless:apply) selectively on specific modules, which is efficient for large projects where you might only need to format certain modules (e.g., during development on a specific submodule).

Prerequisites

Your project uses Maven with a multi-module structure (defined in a parent pom.xml with <modules>...</modules>).
Spotless Maven plugin is configured in your project (typically in the parent POM or individual module POMs). If not, add it to your POM:
```
<build>
  <plugins>
    <plugin>
      <groupId>com.diffplug.spotless</groupId>
      <artifactId>spotless-maven-plugin</artifactId>
      <version>2.43.0</version>  
      <configuration>
        
      </configuration>
    </plugin>
  </plugins>
</build>
```
- Common rules include Google Java Format, Eclipse JDT for Java, or customizations for imports, spacing, etc.
- Spotless supports many file types (Java, Kotlin, XML, etc.) and integrates well with CI tools for pre-commit hooks (via the spotless:check goal, which fails builds on unformatted code).

Using `-pl` to Control Module Formatting

Maven’s -pl (project list) flag lets you specify a comma-separated list of modules to include in the build/plugin execution. By default, Maven runs on all modules, but -pl restricts it, saving time and avoiding unnecessary work on unaffected modules.

Basic Command Structure:
- To check formatting (without applying changes): mvn spotless:check -pl module1,module2
- To apply formatting fixes: mvn spotless:apply -pl module1,module2
- Replace module1,module2 with the actual module names (e.g., relative paths from the root, like core,api).
Examples:
1. Check formatting only on the core module:
```
mvn spotless:check -pl core
```
  - This scans and validates only core’s source files. If any formatting issues exist, the build fails with details (e.g., “Please run spotless:apply to fix”).
2. Apply formatting to multiple modules (api and utils):
```
mvn spotless:apply -pl api,utils
```
  - This modifies files in-place to match your Spotless rules. Always commit changes after to avoid surprises in version control.
3. Exclude specific modules during a full project run: Use -pl !moduleToSkip to run on everything except certain modules (Maven 3.2.1+ supports negation with !).
  - Example: mvn spotless:check -pl !legacy (runs on all modules except legacy).
Tips for Efficiency:
- Parallel Execution: Add -T 4 for multi-threaded builds (e.g., mvn spotless:check -pl core,api -T 4).
- Dry Run: Use spotless:check first to preview issues without changes—it’s idempotent and safe.
- Integration with IDE/Version Control: Configure Spotless to run on save/commit in your IDE (e.g., IntelliJ via Spotless plugin) or use it as a pre-commit hook (via tools like pre-commit or Git hooks) for automated checks.
- Handling Reactor Resolution: If module dependencies are complex, Maven resolves them automatically when using -pl, ensuring dependent modules are processed first if needed.
- Common Issues:
  - If -pl isn’t working, ensure modules are defined in <modules> and use fully qualified paths if there are ambiguities (e.g., -pl :core for multi-repo setups).
  - For Gradle users (if you meant Spotless Gradle plugin instead), the equivalent is -p for project paths, but your query specifies -pl, so Maven is assumed. If it’s Gradle, switch to plugins like gradle task -p submodule.

For full documentation, refer to the Spotless Maven Plugin docs. If your setup differs (e.g., Gradle), provide more details for tailored advice.

Back

x-ai/grok-code-fast-1

Donate