环境

• jdk：java8
• 框架：SpringBoot

代码部分

• Controller

@Autowired
    FileDownloadService downloadService;
    /**
     * 下载文件
     * @param fileKey
     * @param processId
     * @param request
     * @param response
     * @return
     */
//    @RequiresAuthentication
    @RequestMapping("/download")
    public String downloadFile(@RequestParam("fileKey") String fileKey, @RequestParam("processId") String processId, HttpServletRequest request, HttpServletResponse response){
        return downloadService.downLoadFile(fileKey,processId,request,response);
    }

• Service

/**
     * 下载文件
     *
     * @return
     */
    @Override
    public String downLoadFile(String fileKey, String processId,
                               HttpServletRequest request,
                               HttpServletResponse response) {
        RocFileSubmit fileSubmit = fileSubmitMapper.selectByFileKeyAndProcessId(fileKey, processId);
        if (fileSubmit == null) {
            //报异常
            return null;
        }
        //文件路径
        String fileUrl = fileSubmit.getUrl();
        String fileName = fileSubmit.getName();
        logger.info("【下载文件-文件名称】："+fileName);
        return down(fileUrl, fileName, request, response);
    }

    public String down(String fileUrl, String fileName, HttpServletRequest request, HttpServletResponse response) {
        File file = new File(fileUrl);
        if (file.exists()) {
            //解决中文文件名乱码问题
            String userAgent = request.getHeader("User-Agent");
            // 针对IE或者以IE为内核的浏览器：

            if (userAgent.contains("MSIE") || userAgent.contains("Trident")) {
                try {
                    fileName = java.net.URLEncoder.encode(fileName, "UTF-8");
                } catch (UnsupportedEncodingException e) {
                    e.printStackTrace();
                }
            } else {
                // 非IE浏览器的处理：
                try {
                    fileName = new String(fileName.getBytes("UTF-8"), "ISO-8859-1");
                } catch (UnsupportedEncodingException e) {
                    e.printStackTrace();
                }
            }
            response.setHeader("Content-disposition", String.format("attachment; filename=\"%s\"", fileName));
            response.setContentType("multipart/form-data");
            response.setCharacterEncoding("UTF-8");

            byte[] buffer = new byte[1024];
            FileInputStream fis = null;
            BufferedInputStream bis = null;
            try {
                fis = new FileInputStream(file);
                bis = new BufferedInputStream(fis);
                OutputStream os = response.getOutputStream();
                int i = bis.read(buffer);
                while (i != -1) {
                    os.write(buffer, 0, i);
                    i = bis.read(buffer);
                }
//                System.out.println("success");
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                if (bis != null) {
                    try {
                        bis.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                if (fis != null) {
                    try {
                        fis.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
        return null;
    }