An Agent Skill that guides upgrading Java codebases between LTS versions (8 → 11 → 17 → 21 → 25).

Give it a pom.xml, build.gradle, or source files and it will detect the current Java version, audit for removed/deprecated APIs, produce concrete code diffs, update build configuration, flag incompatible dependencies, and deliver a migration checklist — so you can upgrade with confidence instead of guesswork.

1. Detects current and target Java version from build files
2. Audits source code for removed APIs, JPMS issues, and deprecated patterns
3. Updates Maven and Gradle build configuration with diff blocks
4. Refactors code with before/after examples (records, pattern matching, virtual threads, text blocks, etc.)
5. Checks dependencies against a compatibility matrix of 30+ popular libraries
6. Produces a migration summary checklist (blockers → recommended → verification)

This skill follows the Agent Skills open standard and works with any compatible agent.

# Global (all projects)
cp -r java-version-upgrade ~/.claude/skills/

# Per-project
cp -r java-version-upgrade your-project/.claude/skills/

cp -r java-version-upgrade your-project/.github/skills/

cp -r java-version-upgrade your-project/.cursor/skills/

cp -r java-version-upgrade your-project/.codex/skills/

Zip the java-version-upgrade folder and upload it in Settings → Customize → Skills.

The skill triggers automatically when you ask your agent something like:

• "Upgrade this project from Java 8 to 21"
• "We're still on Java 8, what breaks if we move to 17?"
• "Audit this codebase for Java 11 to 21 migration issues"
• "Bump the JDK version to 21 and update the pom.xml"

Or invoke it explicitly with /java-version-upgrade (in agents that support slash commands).

java-version-upgrade/
├── SKILL.md                          # Main skill instructions
├── LICENSE                           # Apache 2.0
├── README.md
└── resources/
    ├── migration-matrix.md           # Overview of all migration paths
    ├── java8-to-11.md                # Blockers, build config, code examples
    ├── java11-to-17.md               # Blockers, build config, code examples
    ├── java17-to-21.md               # Blockers, build config, code examples
    ├── java21-to-25.md               # Blockers, build config, code examples
    └── common-dependencies.md        # Compat matrix for 30+ popular libraries

When given a Maven project on Java 8 targeting Java 17, the skill produces:

• Build config diffs — updated pom.xml with compiler release, plugin versions, and new dependencies (e.g., Jakarta JAXB replacing javax.xml.bind)
• Dependency flags — Lombok 1.18.12 → 1.18.34, Mockito 3.x → 4.x, Jackson 2.11 → 2.14+, etc.
• Code refactoring — pattern matching for instanceof, switch expressions, text blocks, List.of(), String.isBlank()
• Migration checklist — blockers, recommended improvements, and verification steps

Contributions are welcome! Some ideas:

• Add coverage for future LTS versions as they are released
• Expand the dependency compatibility matrix
• Add more code refactoring examples for specific frameworks
• Improve triggering for edge-case prompts

Apache 2.0