Migrating EML‐CTS from Java 8 to Java 21

We moved EML-CTS from Java 8 to Java 21. We made this choice because Java 8 was outdated, and Oracle was no longer providing it with Premier Support. We decided on Java 21 because this was the latest LTS (Long-Term Support) Java version Oracle offered. The Java 21 move also necessitated a move to Spring Boot 3, as Spring Boot 2 did not support Java 21.

Migrations are usually tough due to the large potential for version conflicts and breaking changes with dependencies. Fortunately, those were minimal and the migration only required minor changes to the codebase (such as changing the names of imports). We found no change to the functionality of EML-CTS after the migration.