使用CountDownLatch实现异步转同步

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

public class Application {
    public static void main(String[] args) {
        CountDownLatch countDownLatch = new CountDownLatch(1);

        CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
            try {
                Thread.sleep(2000);
            } catch (Exception e) {
                e.printStackTrace();
            }
            countDownLatch.countDown();

            return "world";
        });

        try {
            if (!countDownLatch.await(1, TimeUnit.SECONDS)) {
                System.out.println("timeout");
            }
            System.out.println(future.get());
        } catch (Exception e) {
            e.printStackTrace();
        }

        System.out.println("done");
    }
}