Java多线程分块下载器

'''java
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardCopyOption;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class MultiThreadDownloader {
private final static int BUFFER_SIZE = 4096;

public static void main(String[] args) throws IOException {
    String fileUrl = "http://www.example.com/largefile.zip";
    Path saveDir = Path.of("downloads");

    int numThreads = 4;
    long fileSize = getFileSize(fileUrl);
    List<DownloadTask> tasks = splitTasks(numThreads, fileSize);

    ExecutorService executor = Executors.newFixedThreadPool(numThreads);

    List<CompletableFuture<Void>> futures = new ArrayList<>();

    for (DownloadTask task : tasks) {
        futures.add(CompletableFuture.runAsync(() -> {
            try {
                downloadChunk(fileUrl, saveDir, task.startPos, task.endPos);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }, executor));
    }

    CompletableFuture.allOf(futures.toArray(new CompletableFuture[0]))
            .thenRun(() -> {
                System.out.println("Download finished!");
                executor.shutdown();
            })
            .exceptionally(ex -> {
                System.err.println("Download failed: " + ex.getMessage());
                executor.shutdown();
                return null;
            });
}

private static void downloadChunk(String fileUrl, Path saveDir, long startPos, long endPos) throws IOException {
    HttpURLConnection connection = (HttpURLConnection) new URL(fileUrl).openConnection();
    connection.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);
    try (InputStream input = connection.getInputStream();
         OutputStream output = new BufferedOutputStream(Files.newOutputStream(saveDir, StandardCopyOption.CREATE, StandardCopyOption.APPEND))) {

        byte[] buffer = new byte[BUFFER_SIZE];
        int bytesRead;
        while ((bytesRead = input.read(buffer)) != -1) {
            output.write(buffer, 0, bytesRead);
        }
    }
}

private static long getFileSize(String fileUrl) throws IOException {
    HttpURLConnection connection = (HttpURLConnection) new URL(fileUrl).openConnection();
    return connection.getContentLengthLong();
}

private static List<DownloadTask> splitTasks(int numThreads, long fileSize) {
    long chunkSize = fileSize / numThreads;
    List<DownloadTask> tasks = new ArrayList<>();
    for (int i = 0; i < numThreads; i++) {
        long startPos = i * chunkSize;
        long endPos = (i == numThreads - 1) ? fileSize - 1 : (startPos + chunkSize - 1);
        tasks.add(new DownloadTask(startPos, endPos));
    }
    return tasks;
}

private static class DownloadTask {
    private final long startPos;
    private final long endPos;

    public DownloadTask(long startPos, long endPos) {
        this.startPos = startPos;
        this.endPos = endPos;
    }
}

}
'''