From Threads to Thousands – How Virtual Threads Are Transforming Java Development

Virtual Threads in Java 21 represent one of the most significant paradigm shifts in recent years. They don’t just change how we handle concurrency – they let us write simpler, more straightforward code without sacrificing scalability. For those of us building Java-based solutions, this is a game changer worth understanding deeply.

Why Traditional Threads Aren’t Enough Anymore

Traditionally, Java (like most languages) has built concurrency on top of operating system (OS) threads. And while that’s worked well for many types of applications, there’s a fundamental issue: OS threads are heavy.

Each thread consumes a noticeable amount of memory and CPU. So, if you need to handle tens of thousands of concurrent connections – say in a modern microservice or API gateway – you typically have two choices:

Use a small number of threads and rely on asynchronous callbacks, or
Allocate lots of resources to keep many threads alive.

Both have drawbacks. Async code (using callbacks or futures) gets messy and hard to debug. And too many threads cause memory pressure and context-switching overhead.

This is where virtual threads come in.

What Are Virtual Threads – And Why Are They Revolutionary?

Virtual threads are ultra-lightweight threads managed by the JVM, not the OS. They can be paused and resumed by the JVM itself, without requiring expensive context switching by the operating system.

This means:

You can run hundreds of thousands of threads in a single JVM process – without hitting heap or CPU limits.
You can write classic, blocking-style code and still achieve extreme scalability.
All modern APIs work as-is – you don’t need to rewrite your REST clients, JDBC calls, or socket code to benefit from virtual threads.

It’s next-level concurrency – without having to sacrifice your code to the asynchronous maze.

A common question: “So do I have to code differently now?”
Answer: No – you can keep writing code the way you always have, but the JVM handles it far more efficiently under the hood.

How Do Virtual Threads Work?

When a virtual thread blocks on an I/O operation (like waiting for a database response), it is detached from its carrier thread (an underlying OS thread), and the JVM schedules other virtual threads on that carrier instead.

In practice, a single OS thread can carry many virtual threads that take turns executing.

During something like a Thread.sleep(), network read, or database query, the JVM can quickly park the idle virtual thread without tying up expensive resources.

The result: Server applications can now handle massive amounts of concurrent requests – something that was either impossible or overly complex with traditional threading models.

Why This Matters for Real-World Development

For us building modern Java solutions – especially in microservices, real-time pipelines, and cloud-based APIs – virtual threads change the game:

Simpler code: We can go back to writing clean, synchronous logic without scalability fears.
Better performance: Systems can handle far more concurrency with lower latency and fewer bottlenecks.
Less technical debt: No need for complex async libraries or reactive rewrites unless absolutely necessary.
Faster development: Synchronous code is easier to write, test, and reason about – and virtual threads reduce the need for thread-safety workarounds or boilerplate.

In short: we can focus on business logic instead of thread wrangling.

A Few Things to Keep in Mind

Virtual threads are powerful – but they’re not magic. Here’s what you need to know:

Blocking is fine – at the right places. If you use older I/O that isn’t integrated with the JVM’s parking logic (e.g., some native libraries), it can still block the OS thread.
Best suited for I/O-bound workloads. Virtual threads won’t boost CPU-bound performance – they shine when waiting on external systems.
Test and profile. They’re fast, but as with any new technology – measure in your environment.

How We Use Virtual Threads at HiQ

At HiQ, we’ve already started using virtual threads in new solutions – especially where we build scalable APIs and cloud services that demand high concurrency. By combining virtual threads with modern frameworks like Spring Boot 3.1+ and new Java language features like pattern matching and records, we’re delivering solutions that are fast, robust, and future-ready.

The best part: We get to write clean, readable code – and still meet today’s scalability demands.

If you’ve read this far, chances are you’re a Java developer curious about what’s next. And you know what? We’d love to meet you. Right now, we’re actively looking for top-tier developers – read more here!