GeezerVison is showing javaevolved.dev — Virtual thread executor | java.evolved

Home / Streams / Virtual thread executor

Streams Intermediate

Virtual thread executor

Use virtual thread executors for unlimited lightweight concurrency.

Code Comparison

✕ Java 8

ExecutorService exec =
    Executors.newFixedThreadPool(10);
try {
    futures = tasks.stream()
        .map(t -> exec.submit(t))
        .toList();
} finally {
    exec.shutdown();
}

✓ Java 21+

try (var exec = Executors
        .newVirtualThreadPerTaskExecutor()) {
    var futures = tasks.stream()
        .map(exec::submit)
        .toList();
}

Share 𝕏

See a problem with this code? Let us know.

Why the modern way wins

♾️

No sizing

No pool size to tune — create as many threads as needed.

⚡

Lightweight

Virtual threads use KB of memory, not MB.

🧹

Auto-closeable

try-with-resources handles shutdown automatically.

Old Approach

Fixed Thread Pool

Modern Approach

Virtual Thread Executor

Since JDK

Difficulty

Intermediate

JDK Support

Virtual thread executor

Available

Widely available since JDK 21 LTS (Sept 2023)

How it works

The virtual thread executor creates a new virtual thread for each task. No pool sizing needed — virtual threads are cheap enough to create millions of them.

Stream gatherers

Java 8

// Sliding window: manual implementation
List<List<T>> windows = new ArrayList<>();
for (int i = 0; i <= list.size()-3; i++) {
    windows.add(
        list.subList(i, i + 3));
}

Java 24+

var windows = stream
    .gather(
        Gatherers.windowSliding(3)
    )
    .toList();

Hover to see modern ➜

JDK 24+ →

Streams Intermediate

Stream.iterate() with predicate

Java 8

Stream.iterate(1, n -> n * 2)
    .limit(10)
    .forEach(System.out::println);
// can't stop at a condition

Java 9+

Stream.iterate(
    1,
    n -> n < 1000,
    n -> n * 2
).forEach(IO::println);
// stops when n >= 1000

Hover to see modern ➜

JDK 9+ →

Streams Beginner

Optional.ifPresentOrElse()

Java 8

Optional<User> user = findUser(id);
if (user.isPresent()) {
    greet(user.get());
} else {
    handleMissing();
}

Java 9+

findUser(id).ifPresentOrElse(
    this::greet,
    this::handleMissing
);

Hover to see modern ➜

JDK 9+ →