spring boot下载文件使用断点续传功能

下载文件时使用断点续传可以很方便的为访问者减少等待时间和流量的大量浪费。

@RequestMapping("/download/{name}")
    public void getDownload(@PathVariable String name, HttpServletRequest request, HttpServletResponse response) throws FileNotFoundException {
        // Get your file stream from wherever.
        logger.info("name="+name);
        String fullPath = ResourceUtils.getURL("classpath:").getPath() + "static/ludashisetup.exe";
        logger.info("下载路径:"+fullPath);
        File downloadFile = new File(fullPath);

        ServletContext context = request.getServletContext();
        // get MIME type of the file
        String mimeType = context.getMimeType(fullPath);
        if (mimeType == null) {
            // set to binary type if MIME mapping not found
            mimeType = "application/octet-stream";
        }

        // set content attributes for the response
        response.setContentType(mimeType);
        // response.setContentLength((int) downloadFile.length());

        // set headers for the response
        String headerKey = "Content-Disposition";
        String headerValue = String.format("attachment; filename="%s"", downloadFile.getName());
        response.setHeader(headerKey, headerValue);
        // 解析断点续传相关信息
        response.setHeader("Accept-Ranges", "bytes");
        long downloadSize = downloadFile.length();
        long fromPos = 0, toPos = 0;
        if (request.getHeader("Range") == null) {
            response.setHeader("Content-Length", downloadSize + "");
        } else {
            // 若客户端传来Range，说明之前下载了一部分，设置206状态(SC_PARTIAL_CONTENT)
            response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);
            String range = request.getHeader("Range");
            String bytes = range.replaceAll("bytes=", "");
            String[] ary = bytes.split("-");
            fromPos = Long.parseLong(ary[0]);
            if (ary.length == 2) {
                toPos = Long.parseLong(ary[1]);
            }
            int size;
            if (toPos > fromPos) {
                size = (int) (toPos - fromPos);
            } else {
                size = (int) (downloadSize - fromPos);
            }
            response.setHeader("Content-Length", size + "");
            downloadSize = size;
        }
        // Copy the stream to the responses output stream.
        RandomAccessFile in = null;
        OutputStream out = null;
        try {
            in = new RandomAccessFile(downloadFile, "rw");
            // 设置下载起始位置
            if (fromPos > 0) {
                in.seek(fromPos);
            }
            // 缓冲区大小
            int bufLen = (int) (downloadSize < 2048 ? downloadSize : 2048);
            byte[] buffer = new byte[bufLen];
            int num;
            int count = 0; // 当前写到客户端的大小
            out = response.getOutputStream();
            while ((num = in.read(buffer)) != -1) {
                out.write(buffer, 0, num);
                count += num;
                //处理最后一段，计算不满缓冲区的大小
                if (downloadSize - count < bufLen) {
                    bufLen = (int) (downloadSize-count);
                    if(bufLen==0){
                        break;
                    }
                    buffer = new byte[bufLen];
                }
            }
            response.flushBuffer();
        } catch (IOException e) {
            logger.info("数据被暂停或中断。");
//            e.printStackTrace();
        } finally {
            if (null != out) {
                try {
                    out.close();
                } catch (IOException e) {
                    logger.info("数据被暂停或中断。");
//                    e.printStackTrace();
                }
            }
            if (null != in) {
                try {
                    in.close();
                } catch (IOException e) {
                    logger.info("数据被暂停或中断。");
//                    e.printStackTrace();
                }
            }
        }
    }