多线程用FileUtils.copyURLToFile下载网图代码

可以实现多线程下载，提高下载速度。具体代码实现可以参考以下示例：

import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class MultiThreadDownloader {
    private static final int THREAD_SIZE = 3; // 线程数
    private static final String URL_PATH = "https://example.com/image.jpg"; // 要下载的文件URL路径
    private static final String FILE_NAME = "image.jpg"; // 下载后保存的文件名
    private static final String FILE_PATH = "D:\\"; // 下载后保存的路径

    public static void main(String[] args) {
        ExecutorService threadPool = Executors.newFixedThreadPool(THREAD_SIZE);
        try {
            URL url = new URL(URL_PATH);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");
            conn.setConnectTimeout(5000);
            int len = conn.getContentLength();
            int block = len % THREAD_SIZE == 0 ? len / THREAD_SIZE : len / THREAD_SIZE + 1;

            for (int i = 0; i < THREAD_SIZE; i++) {
                int start = i * block;
                int end = (i + 1) * block - 1;
                if (i == THREAD_SIZE - 1) {
                    end = len - 1;
                }
                Runnable task = new DownloadTask(url, start, end, FILE_PATH + FILE_NAME);
                threadPool.execute(task);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            threadPool.shutdown();
        }
    }

    static class DownloadTask implements Runnable {
        private URL url;
        private int start;
        private int end;
        private String filePath;

        public DownloadTask(URL url, int start, int end, String filePath) {
            this.url = url;
            this.start = start;
            this.end = end;
            this.filePath = filePath;
        }

        @Override
        public void run() {
            try {
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("GET");
                conn.setConnectTimeout(5000);
                conn.setRequestProperty("Range", "bytes=" + start + "-" + end);
                InputStream is = conn.getInputStream();
                RandomAccessFile raf = new RandomAccessFile(new File(filePath), "rwd");
                raf.seek(start);
                byte[] buffer = new byte[1024];
                int len;
                while ((len = is.read(buffer)) != -1) {
                    raf.write(buffer, 0, len);
                }
                raf.close();
                is.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}