Exploring JDK 21: Virtual Threads, Generational ZGC, and New APIs

This article provides a comprehensive exploration of JDK 21's major features, focusing on virtual threads and generational ZGC as the two most significant additions. The author begins by introducing JDK 21's 15 new features, then delves into virtual threads, explaining how they differ from platform threads and their benefits for I/O-intensive applications.

The article includes detailed performance comparisons between virtual threads and platform threads, demonstrating how virtual threads can handle 10,000 tasks more efficiently using fewer resources. It also addresses the challenges of using ThreadLocal with virtual threads and introduces Scoped Values as a replacement. The author provides practical guidance on monitoring virtual threads and best practices for implementation.

The second major feature, generational ZGC, is explained in detail, showing how it improves upon the previous ZGC by introducing young and old generation collections. Performance comparisons with G1GC and ZGC demonstrate generational ZGC's superior throughput and lower pause times.

The article also covers Spring Boot 3.2.0-M1's support for virtual threads, providing code examples for enabling virtual threads in web applications and Spring Data Redis. Finally, it introduces new APIs in JDK 21, including String templates, record patterns, pattern matching for switch statements, and unnamed patterns and variables.

The author concludes by emphasizing the significance of these features for high-concurrency applications and their potential to improve Java's performance and scalability. The article is based on practical testing on a Mac M1 Pro system and includes references to relevant JDK Enhancement Proposals (JEPs).