// 创建httpclient对象
CloseableHttpClient httpclient;httpclient = HttpClients.createDefault();
// 创建get访问方法的对象
HttpGet httpget = new HttpGet(urL);
// 在请求头中添加Range属性
httpget.addHeader("Range", "bytes=" + block.getBlockstart() + "-" + block.getBlockend());
// 执行get获取响应
HttpResponse response = httpclient.execute(httpget);
// 检查响应码
int status = response.getStatusLine().getStatusCode();
if (!(status >= 200 && status < 300)) {
	throw new ClientProtocolException("Unexpected response status: " + status);
}
// 获取响应实体
HttpEntity entity = response.getEntity();
// 获取报文内容，这时服务器传过来的内容就可以通过输入流得到了
InputStream in = entity.getContent();
if(entity.getContentLength() <= 0) {
    putQueue("No file to download");
    throw new ClientProtocolException("entity.getContentLength() = 0");
}

/**
* 根据文件程度更新块大小
* 将文件切割成块放入list以便分配给各线程
*/
private void initBlock() {
    // 更新块大小
    blocksize = fileLength / (threadNum * 3L);
    blockList = new CopyOnWriteArrayList<>();
    long now = fileLength;
    long blockstart = 0, blockend;
    // 切割文件成块，放入list
    while(now > 0) {
        long len = Math.min(blocksize - 1, now);
        blockend = blockstart + len;
        blockend = Math.min(fileLength, blockend);
        blockList.add(new Block(blockstart, blockend));

        blockstart = blockend + 1;
        now -= blocksize;
    }
}

/**
* 线程控制
* 通过将不同的block分配给不同的task，实现线程的任务分配
*/
private void threadControl() {

    // 倒计时计数器记下当前任务数
    countDownLatch = new CountDownLatch(blockList.size());

    for(Block b : blockList) {
        executor.submit(new DownloadTask(b));
    }

    // 主线程等待待线程同步
    try {
        countDownLatch.await();
    } catch (InterruptedException e) {
        putQueue(e.getMessage());
    }

    // block没有完全remove说明有的block下载失败了，那就再来一遍
    if(!blockList.isEmpty()) {
        threadControl();
    }
}

/**
* 设置内部类实现Runnable完成线程任务
*/
private final class DownloadTask implements Runnable{

    private final Block block;
    private InputStream in = null;

    private DownloadTask(Block b) {
        block = b;
    }
    @Override
    public void run() {
        // 使用RandomAccessFile进行随机读写
        // 并且使用 try-with-resource 实现自动关闭
        try(RandomAccessFile rfile = new RandomAccessFile(filename, "rwd")) {
            // 使用信号量控制线程协同
            semaphore.acquire();
            rfile.seek(block.getBlockstart());

            /*
            ** http操作与文件写入
            */

            blockList.remove(block);

        } catch (Exception e) {
            putQueue(String.format("%s-%s failed, has been added into the download list again.",
                    block.getBlockstart(), block.getBlockend()));
            putQueue(e.getMessage());
        } finally {

            countDownLatch.countDown();
            semaphore.release();

            try {
                if(in != null) {
                    in.close();
                }
            } catch (IOException e) {
                putQueue(e.getMessage());
            }

        }
    }
}

public class DownloadTest {

    @Test
    public void start0() {
        Download d0 = new Download("https://soft.xitongxz.net/202106/FZXGJ_V10.6_XiTongZhiJia.zip",
                8, ".\\download0.zip");
        d0.start();
    }

    @Test
    public void start1() {
        Download d1 = new Download("https://ys-api.mihoyo.com/event/download_porter/link/ys_cn/official/pc_default",
                8, ".\\download1.exe");
        d1.start();
    }

    @Test
    public void start2() {
        Download d2 = new Download("https://count.iuuu9.com/d.php?id=501616&urlos=android",
                8, ".\\download2.apk");
        d2.start();
    }

    @Test
    public void start3() {
        Download d3 = new Download("https://ys-api.mihoyo.com/event/download_porter/link/ys_cn/official/pc_default",
                4, ".\\download3.exe");
        d3.start();
    }

    @Test
    public void start4() {
        Download d4 = new Download("https://ys-api.mihoyo.com/event/download_porter/link/ys_cn/official/pc_default",
                -1, ".\\download4.exe");
        d4.start();
    }

    @Test
    public void start5() {
        Download d5 = new Download("https://ys-api.mihoyo.com/event/download_porter/link/ys_cn/official/pc_default",
                100, ".\\download5.exe");
        d5.start();
    }

    @Test
    public void start6() {
        Download d6 = new Download("111222",
                8, ".\\download6.exe");
        d6.start();
    }

    @Test
    public void start7() {
        Download d7 = new Download("https://www.coder.work/article/4681889",
                8, ".\\download7.exe");
        d7.start();
    }

    @Test
    public void start8() {
        Download d8 = new Download("https://ys-api.mihoyo.com/event/download_porter/link/ys_cn/official/pc_default",
                8, ".\\download1.exe");
        d8.start();
    }

    @Test
    public void start9() {
        Download d9 = new Download("https://ys-api.mihoyo.com/event/download_porter/link/ys_cn/official/pc_default",
                8, ".\\new\\download9.exe");
        d9.start();
    }
}