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Java maven

Skill mtkhawaja/java-skills/skills/java-maven

A Claude Code plugin and marketplace providing a skills library for high-quality Java development.

Install
npx -y skills add mtkhawaja/java-skills --skill java-maven

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Use when working with Maven builds — editing pom.xml, structuring or building multi-module/multi-project (reactor) projects, managing dependencies/plugins/BOMs, cleaning up POM hygiene (scopes, ordering, redundant versions), upgrading Maven 3 to Maven 4, or running large mechanical migrations (Java version, Spring Boot, JUnit upgrades) where OpenRewrite recipes beat hand-editing. Load the reference files for multi-module details and the Maven 4 upgrade.

SKILL.md

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Java Maven

Overview

Docs: Maven Wrapper · POM reference · CI-friendly versions · What's new in Maven 4

The house standard for Maven builds. Everyday conventions, POM hygiene, and migrations live here; multi-module/reactor detail and the Maven 4 upgrade live in references/ (routing table below).

Everyday conventions

  • Use the Maven Wrapper (./mvnw, .mvn/wrapper/maven-wrapper.properties) so everyone builds with the same Maven version. Pin it; don't rely on the machine's installed Maven.
  • Pin every plugin version (in <pluginManagement> at the parent), and pin dependency versions via <dependencyManagement> (or an imported BOM) — never leave versions to chance/transitive resolution. Run mvn versions:display-plugin-updates / display-dependency-updates to review.
  • Prefer mvn verify over mvn clean install. verify runs the full check (incl. integration tests) without polluting the local repo; reserve install for when a downstream local build needs the artifact.
  • CI-friendly versions: use ${revision} for a single source of truth across modules (built-in in Maven 4; needs the flatten plugin in Maven 3 — see the upgrade reference).
  • Know your Maven version. Check .mvn/wrapper/maven-wrapper.properties or mvn -v. Maven 4 requires Java 17 to run (it can still compile to older bytecode via the compiler release). Don't use model-4.1.0-only POM features on a Maven 3 build.
  • Keep pom.xml ordered and minimal; don't duplicate a plugin/dependency declaration (Maven 4 fails the build on duplicates that Maven 3 only warned about).
./mvnw verify                                  # the default full check — not clean install
./mvnw -pl :acme-api -am verify                # one subproject plus everything it depends on
./mvnw versions:display-dependency-updates     # review pins (also: display-plugin-updates)

POM hygiene

Apply these to any POM you write or review:

  • Explicit <groupId> on every plugin; explicit versions everywhere (centralized in *Management) — and conversely, children must not re-declare a version that dependencyManagement/pluginManagement already provides.
  • Never <scope>system</scope> — install the artifact into a repo instead.
  • No prefixless/pom. expressions: ${artifactId}/${pom.version} → ${project.artifactId}/${project.version}.
  • Keep the canonical element order in the POM and the dependency list sorted; keep <scm> in sync with the actual git origin.
  • Run mvn dependency:analyze periodically: fix used-undeclared (add them) and unused-declared (remove them) dependencies.

Automated migrations (OpenRewrite)

For well-known mechanical migrations, don't hand-edit dozens of files — run the matching OpenRewrite recipe, then review the diff and ./mvnw verify:

MigrationRecipe (rewrite.activeRecipes)Artifact
POM cleanup (the hygiene rules above)org.openrewrite.maven.BestPracticesbuilt in
Java upgrade (17/21/25)org.openrewrite.java.migrate.UpgradeToJava21 (also ...UpgradeToJava17/...25)rewrite-migrate-java
Spring Boot upgradeorg.openrewrite.java.spring.boot3.UpgradeSpringBoot_3_5 (Boot 4: boot4.UpgradeSpringBoot_4_0)rewrite-spring
JUnit 4 → 5org.openrewrite.java.testing.junit5.JUnit4to5Migrationrewrite-testing-frameworks
Maven 3 → 4use mvnup instead (ships with Maven 4) — see references/maven-4-upgrade.md—

Invoke the plugin directly (no POM changes); the dryRun goal first writes a rewrite.patch preview:

mvn -U org.openrewrite.maven:rewrite-maven-plugin:run \
  -Drewrite.recipeArtifactCoordinates=org.openrewrite.recipe:rewrite-migrate-java:RELEASE \
  -Drewrite.activeRecipes=org.openrewrite.java.migrate.UpgradeToJava21

Recipes are a starting point, not gospel: review the diff, build, and test before committing.

When to open which reference

SituationRead
Setting up or building part of a multi-module repo; reactor/build-order/BOM questionsreferences/multi-module.md
Moving a build to Maven 4, or asked about <subprojects>, mvnup, model 4.1.0, consumer POMreferences/maven-4-upgrade.md

Red flags — stop

  • Plugin or dependency versions not centralized in <pluginManagement> / <dependencyManagement>, or a child re-declaring a managed version
  • <scope>system</scope>; ${pom.*} or prefixless ${artifactId}-style expressions
  • Relying on the machine's Maven instead of the wrapper
  • Using model-4.1.0 features (<subprojects>, root="true", bom packaging) on a Maven 3 build
  • Duplicate plugin declarations in a POM

Keep looking

Skills are one crate of 328,083. Ordering is by how many stacks a row turns up in, so the top of any crate is what has actually been picked rather than what has the most stars.