jdk21 怎么使用scopedValue

在JDK 21中，Scoped Values是一种新的功能，它允许您在代码块中设置和访问线程本地值。这些值只在代码块中可见，并且在代码块退出时自动清除。下面是一个使用Scoped Values的示例程序：

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Flow;
import java.util.concurrent.SubmissionPublisher;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

public class ScopedValuesExample {

    public static void main(String[] args) throws InterruptedException {
        ExecutorService executor = Executors.newFixedThreadPool(2);

        SubmissionPublisher<Integer> publisher = new SubmissionPublisher<>(executor, Flow.defaultBufferSize());

        AtomicInteger counter = new AtomicInteger();

        publisher.subscribe(new ScopedSubscriber<>(() -> counter.getAndIncrement()));

        publisher.submit(1);
        publisher.submit(2);
        publisher.submit(3);

        publisher.close();

        executor.shutdown();
        executor.awaitTermination(1, TimeUnit.MINUTES);

        System.out.println("Counter value: " + counter.get());
    }

    private static class ScopedSubscriber<T> implements Flow.Subscriber<T> {

        private final Runnable onSubscribe;

        private Flow.Subscription subscription;

        public ScopedSubscriber(Runnable onSubscribe) {
            this.onSubscribe = onSubscribe;
        }

        @Override
        public void onSubscribe(Flow.Subscription subscription) {
            this.subscription = subscription;
            onSubscribe.run();
            subscription.request(1);
        }

        @Override
        public void onNext(T item) {
            System.out.println("Received item: " + item);
            subscription.request(1);
        }

        @Override
        public void onError(Throwable throwable) {
            throwable.printStackTrace();
        }

        @Override
        public void onComplete() {
            System.out.println("Subscription completed");
        }
    }
}

在这个示例程序中，我们创建了一个ScopedSubscriber类，它实现了Flow.Subscriber接口。在onSubscribe方法中，我们设置了Scoped Values，以便在代码块中访问计数器。在onNext方法中，我们打印接收到的项目，并请求下一个项目。在程序的末尾，我们打印计数器的值。