Language Briefing — Java 21 Long-Term Support Release
Oracle released Java 21 (JDK 21) on September 19, 2023, delivering virtual threads, pattern matching, and generational ZGC improvements as the next long-term support platform for enterprise Java workloads.
Executive briefing: Oracle and the OpenJDK community shipped Java 21 on . As a long-term support (LTS) release, Java 21 introduces production-ready virtual threads (Project Loom), pattern matching enhancements, and performance gains across the garbage collector and vector APIs.
Key features
- Virtual threads GA. Project Loom’s lightweight threads reach general availability, dramatically increasing concurrency for server applications with minimal code changes.
- Pattern matching and records. Pattern matching for switch statements (JEP 441) and record patterns (JEP 440) simplify data-centric logic.
- Generational ZGC. The Z Garbage Collector gains generational capabilities (JEP 439), reducing pause times for large heaps.
- Security updates. LTS support ensures quarterly CPU releases and security patches through at least 2028 for Oracle builds.
Implementation guidance
- Compatibility testing. Validate frameworks and application servers against Java 21, paying attention to removed deprecated APIs and preview features.
- Performance benchmarking. Evaluate virtual thread adoption for IO-heavy workloads and monitor heap utilisation with generational ZGC.
- Toolchain updates. Update build pipelines (Maven, Gradle, CI runners) and container images to target Java 21 bytecode and runtime settings.
Enablement moves
- Communicate LTS support timelines to product teams and align upgrade roadmaps before Java 17 exits mainstream support.
- Refresh secure coding standards to cover new language features and preview APIs.
- Coordinate with vendors (application servers, monitoring agents) on Java 21 compatibility matrices.