java简单实现多线程下载

    @Test
    void realizeMultithreadedDownload() throws Exception {
        final String urlString = "https://dldir1.qq.com/weixin/Windows/WeChatSetup.exe";
        final String localPath = "src/main/resources/";
        final int threads = 7;
        File temp = new File(localPath + "temp");
        temp.mkdir();
        final String fileName = urlString.substring(urlString.lastIndexOf('/') + 1);
        final long contentLength = new URL(urlString).openConnection().getContentLengthLong();
        final long mean = contentLength / threads;
        CountDownLatch latch = new CountDownLatch(threads);
        for (int i = 0; i < threads; i++) {
            int j = i;
            new Thread(() -> {
                try (OutputStream outputStream = new FileOutputStream(localPath + "temp/" + fileName + j)) {
                    URLConnection connection = new URL(urlString).openConnection();
                    connection.setRequestProperty("Range", "bytes=" + (j == 0 ? 0 : mean * j + 1) + "-" + (j == threads - 1 ? contentLength : mean * (j + 1)));
                    InputStream inputStream = connection.getInputStream();
                    inputStream.transferTo(outputStream);
                    inputStream.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }
                latch.countDown();
            }).start();
        }
        latch.await();
        OutputStream outputStream = new FileOutputStream(localPath + fileName);
        for (File file : Objects.requireNonNull(temp.listFiles())) {
            InputStream inputStream = new FileInputStream(file);
            inputStream.transferTo(outputStream);
            inputStream.close();
            file.delete();
        }
        outputStream.close();
        temp.delete();
    }