多线程下载文件及进度条java代码示例

以下是一个简单的多线程下载文件并显示进度条的Java代码示例：

import java.io.BufferedInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.URL;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

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

    public static void main(String[] args) {
        String fileUrl = "http://example.com/file.zip";
        String saveDir = "download";

        try {
            downloadFile(fileUrl, saveDir);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void downloadFile(String fileUrl, String saveDir) throws IOException {
        URL url = new URL(fileUrl);
        String fileName = fileUrl.substring(fileUrl.lastIndexOf("/") + 1);

        BufferedInputStream in = new BufferedInputStream(url.openStream());
        FileOutputStream fos = new FileOutputStream(saveDir + "/" + fileName);

        ExecutorService executorService = Executors.newFixedThreadPool(5); // 设置线程池大小为5

        byte[] buffer = new byte[BUFFER_SIZE];
        int bytesRead;
        long downloadedBytes = 0;
        long fileSize = url.openConnection().getContentLength();

        while ((bytesRead = in.read(buffer, 0, BUFFER_SIZE)) != -1) {
            executorService.execute(new DownloadWorker(buffer, bytesRead, fos));
            downloadedBytes += bytesRead;
            printProgress(downloadedBytes, fileSize);
        }

        in.close();
        fos.close();

        executorService.shutdown();
    }

    private static void printProgress(long downloadedBytes, long fileSize) {
        int percent = (int) ((downloadedBytes * 100) / fileSize);
        System.out.print("\rDownloaded: " + percent + "%");
    }

    private static class DownloadWorker implements Runnable {
        private byte[] buffer;
        private int bytesRead;
        private FileOutputStream fos;

        public DownloadWorker(byte[] buffer, int bytesRead, FileOutputStream fos) {
            this.buffer = buffer;
            this.bytesRead = bytesRead;
            this.fos = fos;
        }

        @Override
        public void run() {
            try {
                fos.write(buffer, 0, bytesRead);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

这个示例代码使用了Java的多线程和线程池来实现多线程下载文件。它会创建一个固定大小为5的线程池，每个线程负责读取缓冲区中的数据，并将数据写入文件中。同时，它会计算下载进度并显示在控制台上。