BasicAttachment bAttachment = attachmentService.getById(attachmentId); if (bAttachment == null || StringUtils.isBlank(bAttachment.getUrl())) { throw new Exception("未找到下载文件!"); } File downloadFile = new File(bAttachment.getUrl()); if(!downloadFile.exists()) { throw new Exception("未找到下载文件!"); } long fileLength = downloadFile.length();// 记录文件大小 long pastLength = 0;// 记录已下载文件大小 int rangeSwitch = 0;// 0：从头开始的全文下载；1：从某字节开始的下载（bytes=27000-）；2：从某字节开始到某字节结束的下载（bytes=27000-39000） long contentLength = 0;// 客户端请求的字节总量 String rangeBytes = "";// 记录客户端传来的形如“bytes=27000-”或者“bytes=27000-39000”的内容 RandomAccessFile raf = null;// 负责读取数据 OutputStream os = null;// 写出数据 OutputStream out = null;// 缓冲 int bsize = 1024;// 缓冲区大小 byte b[] = new byte[bsize];// 暂存容器 String range = request.getHeader("Range"); int responseStatus = 206; if (range != null && range.trim().length() > 0 && !"null".equals(range)) {// 客户端请求的下载的文件块的开始字节 responseStatus = javax.servlet.http.HttpServletResponse.SC_PARTIAL_CONTENT; log.info("request.getHeader('Range')=" + range); rangeBytes = range.replaceAll("bytes=", ""); if (rangeBytes.endsWith("-")) { rangeSwitch = 1; rangeBytes = rangeBytes.substring(0, rangeBytes.indexOf('-')); pastLength = Long.parseLong(rangeBytes.trim()); contentLength = fileLength - pastLength; } else { rangeSwitch = 2; String temp0 = rangeBytes.substring(0, rangeBytes.indexOf('-')); String temp2 = rangeBytes.substring(rangeBytes.indexOf('-') + 1); pastLength = Long.parseLong(temp0.trim()); contentLength = Long.parseLong(temp2); } } else { contentLength = fileLength;// 客户端要求全文下载 } // 清除首部的空白行 response.reset(); // 告诉客户端允许断点续传多线程连接下载,响应的格式是:Accept-Ranges: bytes response.setHeader("Accept-Ranges", "bytes"); // 如果是第一次下,还没有断点续传,状态是默认的 200,无需显式设置;响应的格式是:HTTP/1.1 if (rangeSwitch != 0) { response.setStatus(responseStatus); // 不是从最开始下载，断点下载响应号为206 // 响应的格式是: // Content-Range: bytes [文件块的开始字节]-[文件的总大小 - 1]/[文件的总大小] switch (rangeSwitch) { case 1: { String contentRange = new StringBuffer("bytes ") .append(new Long(pastLength).toString()).append("-") .append(new Long(fileLength - 1).toString()) .append("/").append(new Long(fileLength).toString()) .toString(); response.setHeader("Content-Range", contentRange); break; } case 2: { // String contentRange = range.replace("=", " ") + "/" // + new Long(fileLength).toString(); // response.setHeader("Content-Range", contentRange); String contentRange = new StringBuffer("bytes ") .append(new Long(pastLength).toString()).append("-") .append(new Long(fileLength - 1).toString()) .append("/").append(new Long(fileLength).toString()) .toString(); response.setHeader("Content-Range", contentRange); break; } default: { break; } } } else { String contentRange = new StringBuffer("bytes ").append("0-") .append(fileLength - 1).append("/").append(fileLength) .toString(); response.setHeader("Content-Range", contentRange); } try { response.setContentType("video/mp4"); response.setHeader("Content-Length", String.valueOf(contentLength)); os = response.getOutputStream(); out = new BufferedOutputStream(os); raf = new RandomAccessFile(downloadFile, "r"); try { long outLength = 0;// 实际输出字节数 switch (rangeSwitch) { case 0: { } case 1: { raf.seek(pastLength); int n = 0; while ((n = raf.read(b)) != -1) { out.write(b, 0, n); outLength += n; } break; } case 2: { raf.seek(pastLength); int n = 0; long readLength = 0;// 记录已读字节数 while (readLength <= contentLength - bsize) {// 大部分字节在这里读取 n = raf.read(b); readLength += n; out.write(b, 0, n); outLength += n; } if (readLength <= contentLength) {// 余下的不足 1024 个字节在这里读取 n = raf.read(b, 0, (int) (contentLength - readLength)); out.write(b, 0, n); outLength += n; } break; } default: { break; } } log.info("Content-Length为：" + contentLength + "；实际输出字节数：" + outLength); out.flush(); } catch (IOException ie) { // ignore } } catch (Exception e) { e.printStackTrace(); } finally { if (out != null) { try { out.close(); } catch (IOException e) { e.printStackTrace(); } } if (raf != null) { try { raf.close(); } catch (IOException e) { e.printStackTrace(); } } }