文件断点续传（视频播放，大文件下载）

客户端每次请求取大文件部分数据。

浏览器播放mp4视频时，会首先传Range消息头，检测到206状态码，和Content-Range，Accept-Ranges 会自动请求余下数据。后端需要在文件任意偏移量取数据。

参考：

springboot项目实现断点续传功能_java_脚本之家

springboot大文件上传、分片上传、断点续传、秒传的实现_java_脚本之家

springboot 大文件上传、分片上传、断点续传、秒传_getmodelrw-优快云博客

https://juejin.cn/post/7387915277318520869

在SpringBoot中实现断点续传的实例代码_java_脚本之家

 主要代码：

    private void videoPlayRange(String taskCode, String fileName) {
        File file = getVideoFile(taskCode, fileName);

        long fileLength = file.length();
        String range = request.getHeader("Range");
        long start = 0, end = fileLength - 1;

        if (range != null) {
            String[] ranges = range.replace("bytes=", "").split("-");
            start = Long.parseLong(ranges[0]);
            end = Math.min(fileLength - 1,start + maxPartSize*1024*1024-1);
            end = ranges.length > 1 ? Long.parseLong(ranges[1]) : end;
        }

        // Set the content type and attachment header.
//            String contentType = request.getServletContext().getMimeType(video.getFile().getAbsolutePath());
        response.setContentType("video/mp4");
//        response.setHeader(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=" + fileName);
        response.setHeader(HttpHeaders.ACCEPT_RANGES, "bytes");
        response.setHeader(HttpHeaders.CONTENT_RANGE, "bytes " + start + "-" + end + "/" + fileLength);
        response.setHeader(HttpHeaders.CONTENT_LENGTH, String.valueOf(end - start + 1));
        response.setStatus(206);
//            headers.setContentType(MediaType.parseMediaType(contentType));

        // Create resource that represents the part of the video file.
        try (RandomAccessFile raf = new RandomAccessFile(file, "r")){
            raf.seek(start);
            ServletOutputStream out = response.getOutputStream();
            byte[] bytes = new byte[4096];
            int r = 0;
            while (start<=end) {
                r = raf.read(bytes,0,(int)Math.min(bytes.length,end-start+1));
                if(r<=0){
                    break;
                }
                start+=r;
                out.write(bytes,0,r);
            }
        } catch (Exception e) {
            throw new RuntimeException(e);
        }

    }