Java 21 Virtual Threads

Virtual threads in Java 21 enable millions of concurrent threads without the overhead of platform threads.

Virtual Threads¶

// Creating a virtual thread Thread.startVirtualThread(() -> { var result = fetchFromDB(); process(result); }); // ExecutorService with virtual threads try (var executor = Executors.newVirtualThreadPerTaskExecutor()) { List> futures = urls.stream() .map(url -> executor.submit(() -> fetch(url))) .toList(); for (var future : futures) { System.out.println(future.get()); } }

Spring Boot Integration¶

Java 21 Virtual Threads¶

spring.threads.virtual.enabled=true

All request handlers run on virtual threads!¶

When to Use¶

• I/O-bound operations (HTTP, DB, file)
• High number of concurrent requests
• NOT for CPU-bound operations
• NOT for synchronized blocks (pinning)

Key Takeaway¶

Virtual threads = millions of concurrent threads. spring.threads.virtual.enabled=true and you’re done. Watch out for synchronized.