java实现一个简单的多线程的文件下载器

Java 中可以使用多线程来实现文件下载器。下面是一个简单的示例代码：

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

public class FileDownloader {
    private static final int THREAD_COUNT = 5;
    private static final String FILE_URL = "https://example.com/file.zip";
    private static final String FILE_NAME = "file.zip";

    public static void main(String[] args) throws IOException {
        ExecutorService executor = Executors.newFixedThreadPool(THREAD_COUNT);
        URL url = new URL(FILE_URL);
        long fileSize = url.openConnection().getContentLengthLong();
        long partSize = fileSize / THREAD_COUNT;

        for (int i = 0; i < THREAD_COUNT; i++) {
            long startByte = i * partSize;
            long endByte = (i + 1) * partSize - 1;
            if (i == THREAD_COUNT - 1) {
                endByte = fileSize - 1;
            }
            executor.execute(new DownloadThread(FILE_NAME, FILE_URL, startByte, endByte));
        }
        executor.shutdown();
    }

    private static class DownloadThread implements Runnable {
        private String fileName;
        private String fileUrl;
        private long startByte;
        private long endByte;

        public DownloadThread(String fileName, String fileUrl, long startByte, long endByte) {
            this.fileName = fileName;
            this.fileUrl = fileUrl;
            this.startByte = startByte;
            this.endByte = endByte;
        }

        @Override
        public void run() {
            try (InputStream in = new URL(fileUrl).openStream();
                 FileOutputStream out = new FileOutputStream(fileName)) {
                in.skip(startByte);
                byte[] buffer = new byte[1024];
                int read;
                while (startByte < endByte && (read = in.read(buffer)) != -1) {
                    out.write(buffer, 0, read);
                    startByte += read;
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

其中，使用 ExecutorService 来管理线程，并使用多个线程下载文件的不同部分。每个线程都使用 URL 和 HTTP 协议来下载文件的一部分，最后将所有部分合并