Skipping Unchanged Maven Modules | Generated by AI

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Question: How can I skip or opt out of a Maven module during a build to speed up the build process, especially if the module hasn’t changed? Suppose I have a project like PAUWeb with Angular frontend, Java 8 backend, and 10 modules, and one module contributes 2 minutes to a 6-minute build.

Answer:

Yes, skipping modules that haven’t changed can speed up your Maven build significantly. There are several strategies you can use in Maven to “opt out” or skip certain modules:

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1. Use the -pl (projects) and -am (also make) flags

Maven allows you to build only specific modules with -pl (projects list). For example:

# Build only moduleA and moduleB
mvn clean install -pl moduleA,moduleB

• -pl specifies which modules to include.
• -am (also make) tells Maven to also build dependencies of the specified modules.

Example skipping a module:

If moduleX takes 2 minutes and hasn’t changed:

mvn clean install -pl !moduleX

• The ! excludes the module.

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2. Use maven.test.skip or skipTests

If your build is slow because of tests in a module, you can skip tests:

mvn install -DskipTests

• Saves time if the module code hasn’t changed but tests take long.

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3. Use -am with selective builds

If modules are interdependent, building only changed modules with -pl + -am ensures dependencies are also built:

mvn install -pl moduleA -am

This builds moduleA and any modules it depends on, skipping unrelated modules.

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4. Incremental Builds / mvn reactor

Maven doesn’t automatically skip unchanged modules by default. To handle that:

• Use takari-lifecycle-plugin or maven-incremental-build tools.
• Some CI/CD systems (like Jenkins) can track which modules changed using Git and trigger Maven builds only for those modules.

Example with incremental plugin:

<plugin>
  <groupId>io.takari.maven.plugins</groupId>
  <artifactId>takari-lifecycle-plugin</artifactId>
  <version>1.13.6</version>
</plugin>

This allows building only changed modules.

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5. Angular frontend optimization

If Angular build is part of the module:

• Consider building Angular separately and only trigger Maven when Java code changes.
• Use ng build --watch or incremental builds to avoid rebuilding every time.

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6. Profile-based skipping

You can define Maven profiles to skip certain modules:

<profiles>
  <profile>
    <id>skip-moduleX</id>
    <modules>
      <module>module1</module>
      <module>module2</module>
      <!-- do not include moduleX -->
    </modules>
  </profile>
</profiles>

Then:

mvn clean install -Pskip-moduleX

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Recommendation for your case:

• Identify slow module (moduleX) → check if code changed.
• Use:

mvn install -pl !moduleX

• Combine with -DskipTests if tests are slow.
• For Angular parts, consider building separately to avoid full rebuild.

This can reduce your build from 6 minutes to ~4 minutes if moduleX hasn’t changed.

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References:

• Maven Reactor Options (-pl and -am)
• Skipping Tests in Maven
• Maven Multi-module Build Tips

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If you want, I can show a ready-to-use Maven command for PAUWeb that skips unchanged modules automatically based on Git diffs. That can save you several minutes per build. Do you want me to do that?

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