Description

This PR establishes the Java 21 foundation for Apache CloudStack 4.22.0.0. From a single instruction, the migration was analyzed across 7,655 Java files in 13 modules, the JDK version was bumped, a sandbox build was verified, test compatibility was checked (discovering a critical cglib blocker), and CI workflows were updated.

Changes:

1. JDK version bump — cs.jdk.version 11 → 21 in root pom.xml
2. CI workflow update — build.yml JDK 17 → 21; trigger-package-and-publish.yml Apache license header added + trailing whitespace fixed
3. Migration status document — JAVA_21_MIGRATION_STATUS.md with module-by-module analysis, deprecated API inventory (9 categories, 1,775+ files affected), and critical blocker documentation

Key finding: cglib-nodep 3.3.0 (unmaintained since 2019) causes Unsupported class file major version 65 errors in 64+ DAO test classes. Migration to ByteBuddy is required before full test suite passes.

Sandbox verification:

• BUILD SUCCESS: 25 modules compiled with JDK 21 in 1:08 min
• Test blocker: VMInstanceDaoImplTest — 18/18 errors due to cglib incompatibility

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Enhancement (improves an existing feature and functionality)
• Cleanup (Code refactoring and cleanup, that may add test cases)
• Build/CI
• Test (unit or integration test code)

Feature/Enhancement Scale or Bug Severity

Feature/Enhancement Scale

• Major
• Minor

Screenshots (if appropriate):

BUILD SUCCESS with JDK 21 (25 modules):

Test compatibility check — cglib blocker discovered:

How Has This Been Tested?

• Sandbox build: mvn install -DskipTests -Dcheckstyle.skip=true -pl server -am with JDK 21 — BUILD SUCCESS (25 modules)
• Test compatibility: mvn test -pl engine/schema -Dtest=VMInstanceDaoImplTest — confirmed cglib blocker (18 errors, major version 65)
• Pre-commit hooks: All 3 commits passed pre-commit validation

How did you try to break this feature and the system with this change?

Ran targeted test against the most critical module (engine/schema) to verify JDK 21 compatibility at the test level. Discovered and documented the cglib-nodep blocker that affects 64+ test classes across the DAO layer.

Link to Devin session: https://app.devin.ai/sessions/fced28320b1b46e2a2f93e712c14677d
Requested by: @hitomimimi