如何解决SpringBoot大文件RestTemplate下载

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近期基于项目上使用到的RestTemplate下载文件流，遇到1G以上的大文件，下载需要3-4分钟，因为调用API接口没有做分片与多线程， 文件流全部采用同步方式加载，性能很慢。最近结合网上案例及自己总结，写了一个分片下载tuling/fileServer项目：

1.包含同步下载文件流在浏览器加载输出相关代码； 2.包含分片多线程下载分片文件及合并文件相关代码；

同步下载，支持分片下载Range主要代码：

@Controllerpublic class DownLoadController {    private static final String UTF8 = "UTF-8";    @RequestMapping("/download")    public void downLoadFile(HttpServletRequest request, HttpServletResponse response) throws IOException {        File file = new File("D:\\DevTools\\ideaIU-2021.1.3.exe");        response.setCharacterEncoding(UTF8);        InputStream is = null;        OutputStream os = null;        try {            // 分片下载 Range表示方式 bytes=100-1000  100-            long fSize = file.length();            response.setContentType("application/x-download");            String fileName = URLEncoder.encode(file.getName(), UTF8);            response.addHeader("Content-Disposition", "attachment;filename=" + fileName);            // 支持分片下载            response.setHeader("Accept-Range", "bytes");            response.setHeader("fSize", String.valueOf(fSize));            response.setHeader("fName", fileName);            long pos = 0, last = fSize - 1, sum = 0;            if (null != request.getHeader("Range")) {                response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);                String numberRange = request.getHeader("Range").replaceAll("bytes=", "");                String[] strRange = numberRange.split("-");                if (strRange.length == 2) {                    pos = Long.parseLong(strRange[0].trim());                    last = Long.parseLong(strRange[1].trim());                    if (last > fSize-1) {                        last = fSize - 1;                    }                } else {                    pos = Long.parseLong(numberRange.replaceAll("-", "").trim());                }            }            long rangeLength = last - pos + 1;            String contentRange = new StringBuffer("bytes").append(pos).append("-").append(last).append("/").append(fSize).toString();            response.setHeader("Content-Range", contentRange);            response.setHeader("Content-Length", String.valueOf(rangeLength));            os = new BufferedOutputStream(response.getOutputStream());            is = new BufferedInputStream(new FileInputStream(file));            is.skip(pos);            byte[] buffer = new byte[1024];            int length = 0;            while (sum < rangeLength) {                int readLength = (int) (rangeLength - sum);                length = is.read(buffer, 0, (rangeLength - sum) <= buffer.length ? readLength : buffer.length);                sum += length;                os.write(buffer,0, length);            }            System.out.println("下载完成");        }finally {            if (is != null){                is.close();            }            if (os != null){                os.close();            }        }    }}

多线程分片下载分片文件，下载完成之后合并分片主要代码：

@RestControllerpublic class DownloadClient {    private static final Logger LOGGER = LoggerFactory.getLogger(DownloadClient.class);    private final static long PER_PAGE = 1024L * 1024L * 50L;    private final static String DOWN_PATH = "F:\\fileItem";    ExecutorService taskExecutor = Executors.newFixedThreadPool(10);    @RequestMapping("/downloadFile")    public String downloadFile() {        // 探测下载        FileInfo fileInfo = download(0, 10, -1, null);        if (fileInfo != null) {            long pages =  fileInfo.fSize / PER_PAGE;            for (long i = 0; i <= pages; i++) {                Future future = taskExecutor.submit(new DownloadThread(i * PER_PAGE, (i + 1) * PER_PAGE - 1, i, fileInfo.fName));                if (!future.isCancelled()) {                    try {                        fileInfo = future.get();                    } catch (InterruptedException | ExecutionException e) {                        e.printStackTrace();                    }                }            }            return System.getProperty("user.home") + "\\Downloads\\" + fileInfo.fName;        }        return null;    }    class FileInfo {        long fSize;        String fName;        public FileInfo(long fSize, String fName) {            this.fSize = fSize;            this.fName = fName;        }    }    /**     * 根据开始位置/结束位置     * 分片下载文件，临时存储文件分片     * 文件大小=结束位置-开始位置     *     * @return     */    private FileInfo download(long start, long end, long page, String fName) {        File dir = new File(DOWN_PATH);        if (!dir.exists()) {            dir.mkdirs();        }        // 断点下载        File file = new File(DOWN_PATH, page + "-" + fName);        if (file.exists() && page != -1 && file.length() == PER_PAGE) {            return null;        }        try {            HttpClient client = HttpClients.createDefault();            HttpGet httpGet = new HttpGet("http://127.0.0.1:8080/download");            httpGet.setHeader("Range", "bytes=" + start + "-" + end);            HttpResponse response = client.execute(httpGet);            String fSize = response.getFirstHeader("fSize").getValue();            fName = URLDecoder.decode(response.getFirstHeader("fName").getValue(), "UTF-8");            HttpEntity entity = response.getEntity();            InputStream is = entity.getContent();            FileOutputStream fos = new FileOutputStream(file);            byte[] buffer = new byte[1024];            int ch;            while ((ch = is.read(buffer)) != -1) {                fos.write(buffer, 0, ch);            }            is.close();            fos.flush();            fos.close();            // 最后一个分片            if (end - Long.parseLong(fSize) > 0) {                // 开始合并文件                mergeFile(fName, page);            }            return new FileInfo(Long.parseLong(fSize), fName);        } catch (IOException e) {            e.printStackTrace();        }        return null;    }    private void mergeFile(String fName, long page) {        File file = new File(DOWN_PATH, fName);        try {            BufferedOutputStream os = new BufferedOutputStream(new FileOutputStream(file));            for (long i = 0; i <= page; i++) {                File tempFile = new File(DOWN_PATH, i + "-" + fName);                while (!file.exists() || (i != page && tempFile.length() < PER_PAGE)) {                    try {                        Thread.sleep(100);                    } catch (InterruptedException e) {                        e.printStackTrace();                    }                }                byte[] bytes = FileUtils.readFileToByteArray(tempFile);                os.write(bytes);                os.flush();                tempFile.delete();            }            File testFile = new File(DOWN_PATH, -1 + "-null");            testFile.delete();            os.flush();            os.close();        } catch (IOException e) {            e.printStackTrace();        }    }    /**     * 获取远程文件尺寸     */    private long getRemoteFileSize(String remoteFileUrl) throws IOException {        long fileSize = 0;        HttpURLConnection httpConnection = (HttpURLConnection) new URL(remoteFileUrl).openConnection();        //使用HEAD方法        httpConnection.setRequestMethod("HEAD");        int responseCode = httpConnection.getResponseCode();        if (responseCode >= 400) {            LOGGER.debug("Web服务器响应错误!");            return 0;        }        String sHeader;        for (int i = 1;; i++) {            sHeader = httpConnection.getHeaderFieldKey(i);            if (sHeader != null && sHeader.equals("Content-Length")) {                LOGGER.debug("文件大小ContentLength:" + httpConnection.getContentLength());                fileSize = Long.parseLong(httpConnection.getHeaderField(sHeader));                break;            }        }        return fileSize;    }    class DownloadThread implements Callable {        long start;        long end;        long page;        String fName;        public DownloadThread(long start, long end, long page, String fName) {            this.start = start;            this.end = end;            this.page = page;            this.fName = fName;        }        @Override        public FileInfo call() {            return download(start, end, page, fName);        }    }}

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