Spring Boot Migrator

Automates Spring Boot 2.x → 3.x migration with JDK 8 → 21 upgrade using OpenRewrite.

What This Skill Does

• ✅ Automated Spring Boot 2 → 3 upgrade (up to 3.5.x)
• ✅ JDK 8 → 21 migration
• ✅ javax. → jakarta. namespace migration
• ✅ Hibernate 5 → 6 adaptation
• ✅ Configuration property updates
• ✅ Dependency version resolution
• ✅ Full validation and testing workflow

Prerequisites Check

Before starting, verify:

java -version    # Need JDK 17+ to run OpenRewrite
mvn -version     # Need Maven 3.8.1+

If missing, guide user to install or offer to create installation script.

Workflow

1. Quick Assessment

Ask user for project path, then analyze:

cd <project-path>
# Check if Maven project
test -f pom.xml || { echo "Not a Maven project"; exit 1; }

# Extract key info
grep -oP '(?<=<spring-boot.version>)[^<]+' pom.xml
grep -oP '(?<=<java.version>)[^<]+' pom.xml
grep -c "<parent>" pom.xml

Confirm with user:

• Current Spring Boot version
• Current Java version
• Parent POM situation (spring-boot-starter-parent vs custom)
• Kotlin detected? (warn about limited support)

2. Pre-Migration Backup

# Create backup branch
git checkout -b backup-before-sb3-$(date +%Y%m%d)
git add -A && git commit -m "Backup before Spring Boot 3 migration" --allow-empty

# Record baseline
mkdir .migration-validation
mvn dependency:tree > .migration-validation/deps-before.txt
mvn clean test > .migration-validation/test-before.txt 2>&1

3. Configure OpenRewrite

Add to pom.xml in <build><plugins>:

<plugin>
    <groupId>org.openrewrite.maven</groupId>
    <artifactId>rewrite-maven-plugin</artifactId>
    <version>5.47.0</version>
    <configuration>
        <activeRecipes>
            <recipe>org.openrewrite.java.spring.boot3.UpgradeSpringBoot_3_3</recipe>
            <recipe>org.openrewrite.java.migrate.UpgradeToJava21</recipe>
            <recipe>org.openrewrite.java.migrate.jakarta.JavaxToJakarta</recipe>
        </activeRecipes>
    </configuration>
    <dependencies>
        <dependency>
            <groupId>org.openrewrite.recipe</groupId>
            <artifactId>rewrite-spring</artifactId>
            <version>5.22.0</version>
        </dependency>
        <dependency>
            <groupId>org.openrewrite.recipe</groupId>
            <artifactId>rewrite-migrate-java</artifactId>
            <version>2.28.0</version>
        </dependency>
    </dependencies>
</plugin>

For custom parent POM projects: See [references/custom-parent-strategy.md](references/custom-parent-strategy.md)

4. Preview Changes

# Discover applicable recipes
mvn rewrite:discover

# Dry run (preview only)
mvn rewrite:dryRun | tee .migration-validation/dryrun.txt

Show user the affected files. Confirm before proceeding.

5. Apply Migration

# Apply changes
mvn rewrite:run | tee .migration-validation/rewrite.txt

# Show what changed
git diff --stat
git diff > .migration-validation/changes.diff

6. Fix Compilation Issues

mvn clean compile 2>&1 | tee .migration-validation/compile-after.txt

Common issues and fixes: See [references/common-fixes.md](references/common-fixes.md)

Auto-detect and suggest fixes for:

• package javax not found → Check third-party deps for Jakarta versions
• PostgreSQL10Dialect missing → Use generic PostgreSQLDialect
• server.max-http-header-size → Rename to server.max-http-request-header-size

Max 3 retry attempts. If still failing after fixes, provide detailed troubleshooting guide.

7. Validate Migration

# Run tests
mvn test | tee .migration-validation/test-after.txt

# Compare dependencies
mvn dependency:tree > .migration-validation/deps-after.txt
diff .migration-validation/deps-before.txt .migration-validation/deps-after.txt > .migration-validation/deps-diff.txt

Generate migration report in .migration-validation/REPORT.md with:

• Before/after comparison
• Test results
• Dependency changes
• Manual follow-up items

Custom Parent POM Handling

For projects with custom parent POMs managing Spring Boot and internal library versions:

Option 1: Update parent POM first (if maintainable) Option 2: Switch to BOM import pattern (recommended)

See [references/custom-parent-strategy.md](references/custom-parent-strategy.md) for detailed implementation.

Manual Follow-Up Checklist

After successful migration, remind user to:

• Review .migration-validation/REPORT.md
• Check application.properties/yml for deprecated properties
• Update CI/CD to use JDK 21
• Test critical business flows manually
• Review third-party library versions for Jakarta compatibility
• Consider enabling Virtual Threads (JDK 21): spring.threads.virtual.enabled=true
• Update Docker base images to JDK 21

Troubleshooting

OpenRewrite fails to run:

# Clear Maven cache
rm -rf ~/.m2/repository/org/openrewrite
mvn rewrite:discover

Recipe not found:

• Check plugin dependency versions are latest
• Verify recipe names with mvn rewrite:discover

Compilation fails after 3 attempts:

• Save all logs to .migration-validation/
• Point user to [references/common-fixes.md](references/common-fixes.md)
• Offer to search Stack Overflow for specific error patterns

Scripts

Use scripts/migrate.sh for fully automated execution when user wants hands-off migration:

# From skill directory
./scripts/migrate.sh <project-path>

The script runs all 10 steps automatically with interactive confirmations at key points.

References

• Custom Parent POM Strategy: [references/custom-parent-strategy.md](references/custom-parent-strategy.md)
• Common Fixes: [references/common-fixes.md](references/common-fixes.md)
• Detailed Research: [references/research.md](references/research.md) - Official tools, migration notes, breaking changes

Success Criteria

Migration is complete when:

• ✅ mvn clean compile succeeds
• ✅ mvn test passes (or user acknowledges expected failures)
• ✅ Migration report generated
• ✅ User informed of manual follow-up items