Upgrading an Older Grails Application

Planning the Upgrade

Upgrading from Grails 3/4 to 5/6/7 requires careful planning. The upgrade process involves updating dependencies, fixing deprecated features, and testing thoroughly.

Pre-Upgrade Checklist

• Run your existing tests and ensure they pass
• Review the Grails upgrade guide for breaking changes
• Update JDK to version 11 or higher (17 recommended)
• Check plugin compatibility with the target version

Step-by-Step Upgrade

# 1. Update the Grails version in gradle.properties
# grailsVersion=5.0.0
# gradleVersion=7.6

# 2. Update the Grails wrapper
gradlew wrapper --gradle-version 7.6

# 3. Update dependencies
gradlew dependencies --refresh-dependencies

# 4. Fix compilation errors
# 5. Run tests
gradlew test

Common Breaking Changes

• Package renames (some utility classes moved)
• Deprecated method removal
• Gradle plugin updates required
• Spring Boot version incompatibilities

Testing After Upgrade

# Run full test suite
gradlew test

# Run integration tests
gradlew integrationTest

# Check for deprecation warnings
gradlew compileGroovy 2>&1 | grep -i deprecat

Key Points

• Always run existing tests before starting the upgrade.
• Upgrade one major version at a time if possible.
• Update JDK, Gradle, and all plugins together.
• Check plugin compatibility before upgrading.
• Thorough testing is essential after any upgrade.