Advanced.java

import java.util.concurrent.atomic.*;
import java.util.concurrent.*;

public final class Advanced {
    /** Uses `Server.uploadBatch` to upload the given texts, or cancels if 2 seconds have elapsed */
    public static CompletableFuture<Void> upload(String[] texts) {
        var cancelFlag = new AtomicBoolean(false);
        return Server.uploadBatch(texts, cancelFlag)
                     .orTimeout(2, TimeUnit.SECONDS)
                     .exceptionally(e -> {
                         cancelFlag.set(true);
                         return null;
                     });
    }

    /** Adapts `OldServer.download` to the `CompletableFuture`-based world,
        and prints the result if successful. */
    public static CompletableFuture<Void> download() {
        var future = new CompletableFuture<String>();
        OldServer.download(future::complete, future::completeExceptionally);
        return future.thenAccept(System.out::println);
    }

    /** Retries `download` until it succeeds */
    public static CompletableFuture<Void> reliableDownload() {
        return download().exceptionallyCompose(e -> reliableDownload());
    }
}