Tags: #java #virtualthreads #loom #performance #springboot #backend

With the release of Java 21+, Virtual Threads (Project Loom) are here to simplify concurrent programming and dramatically improve performance for I/O-heavy applications.

In this post, we’ll explore what virtual threads are, why you should care, and how to use them with real-world Java code examples.

🤔 What Are Virtual Threads?

Virtual threads are lightweight threads managed by the Java Virtual Machine (JVM), not the OS.

Unlike traditional platform threads (which map 1:1 to native OS threads), virtual threads allow thousands—even millions—of concurrent tasks to run without blocking expensive resources.

🚀 Why Use Virtual Threads?

Benefit Explanation
Lightweight Concurrency You can spawn 1M+ threads without crashing your system
Simplified Code No need for complex thread pooling logic
Non-blocking by Default Ideal for IO-bound services (e.g., HTTP, DB calls)
Compatibility Works with existing Java APIs

🧪 Real-World Example: REST API with Virtual Threads

Let’s build a Spring Boot REST API that handles incoming HTTP requests using virtual threads.

☕ Java 21 Setup

Make sure your pom.xml or build.gradle is targeting Java 21+.

✅ Configuration in Spring Boot 3.2+ 

@Bean
public TaskExecutor applicationTaskExecutor() {
    return new SimpleAsyncTaskExecutor("virtual-thread-") {{
        setVirtualThreads(true);
    }};
}

🧵 Sample Controller Using Virtual Threads 

@RestController
public class VirtualThreadController {

    @GetMapping("/process")
    public Callable<String> handleRequest() {
        return () -> {
            Thread.sleep(2000); // Simulate I/O task
            return "Handled by: " + Thread.currentThread();
        };
    }
}

Output:

Handled by: VirtualThread[#35]/runnable@ForkJoinPool

📊 Benchmark: Virtual vs Platform Threads

Scenario Platform Threads Virtual Threads
10,000 Requests High CPU/memory Smooth, scalable
Thread Pool Needed Yes Optional (or minimal)
Blocking I/O Penalty High Handled efficiently

🧠 Where to Use Virtual Threads

  • ✅ Web applications (REST, GraphQL, etc.)
  • ✅ Database-heavy microservices
  • ✅ Concurrent data processing
  • ✅ Server-side batch jobs

🚫 When Not to Use Virtual Threads

  • ❌ Tight CPU-bound loops (use platform threads here)
  • ❌ Libraries using native thread-local storage
  • ❌ Time-sensitive real-time systems

🔄 Migration Tip: Switch Executors

Want to try virtual threads in an existing app?
Just switch to Executors.newVirtualThreadPerTaskExecutor():

ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();

Use it wherever you previously used Executors.newFixedThreadPool().

✨ Final Thoughts

Virtual Threads are a game-changer for scalable Java applications.
You get thread-per-request simplicity without the traditional cost of native threads.

Ready to modernize your backend? Try replacing your executor or Spring Boot thread pool with virtual threads today. ✅

💬 Have you tried Virtual Threads yet? Share your experience or ask questions below!

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