图片下载public String fileDownload(MultipartFile file,Long attachmentId,HttpServletResponse response) throws Exception { //需求，通过id找到文件，读取下载到桌面 //1.通过id找到图片文件 FndAppAttachment date = fndAppAttachmentMapper.getByIdAtmAttachment(attachmentId); //2.读取图片 InputStream is = new ByteArrayInputStream(date.getContent()); response.setContentType("image/**"); try { //通过文件流将图片传给前端 ServletOutputStream out = response.getOutputStream(); int len = 0; byte[] buf = new byte[1024]; //使用一个输入流从buffer里吧数据读出来 while ((len=is.read(buf,0,1024))!=1) { //用输出流往buffer里写数据，中间参数代表从哪个位置读，len代表读取的长度 out.write(buf,0,len); } out.flush(); out.close(); return "下载成功"; }catch(IOException e) { e.getMessage(); } return "下载失败";