java多线程断点续传下载

Java多线程断点续传下载可以使用Java中的线程池和RandomAccessFile类实现。具体步骤如下：

1. 创建一个线程池，线程数量可以根据需要调整。

ExecutorService executorService = Executors.newFixedThreadPool(threadCount);

2. 获取文件大小和已经下载的字节数，计算出每个线程需要下载的字节数。

URL url = new URL(fileUrl);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
long fileSize = connection.getContentLength();
long threadSize = fileSize / threadCount;

3. 创建一个RandomAccessFile对象，指定文件名和读写模式。

RandomAccessFile randomAccessFile = new RandomAccessFile(fileName, "rw");

4. 为每个线程创建一个DownloadThread对象，指定线程编号、起始位置和结束位置。

for (int i = 0; i < threadCount; i++) {
    long start = i * threadSize;
    long end = (i == threadCount - 1) ? fileSize - 1 : start + threadSize - 1;
    DownloadThread thread = new DownloadThread(fileUrl, randomAccessFile, start, end);
    executorService.execute(thread);
}

5. 在DownloadThread中使用HttpURLConnection下载文件，使用RandomAccessFile写入文件。

URL url = new URL(fileUrl);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestProperty("Range", "bytes=" + start + "-" + end);
InputStream inputStream = connection.getInputStream();
byte[] buffer = new byte[1024];
int length;
while ((length = inputStream.read(buffer)) != -1) {
    randomAccessFile.write(buffer, 0, length);
}
inputStream.close();

6. 在程序关闭时，关闭RandomAccessFile和线程池。

randomAccessFile.close();
executorService.shutdown();

这样就可以实现Java多线程断点续传下载了。