springMVC 实现上传文件和下载文件

第一步：
在applicationContext.xml中添加支持
<!-- 支持文件上传 -->
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
</bean>

第二步:

/**
     * 上传文件
     *
     * @param file
     * @param request
     * @param model
     * @return
     */
    @RequestMapping(value = "/upload")
    public String upload(@RequestParam(value = "file", required = false) MultipartFile file, HttpServletRequest request, ModelMap model) {
        //如果文件为空则返回uploadTxt.jsp
        if (file.isEmpty()) {
            return "uploadTxt";
        }
        System.out.println("start upload file");
        String path = request.getSession().getServletContext().getRealPath("upload");
        String fileName = file.getOriginalFilename();
//        //如果文件格式不是txt，返回uploadTxt.jsp
//        if (!fileName.endsWith("txt")) {
//            return "uploadTxt";
//        }
        System.out.println("fileName====>  " + fileName);
//        String fileName = new Date().getTime()+".jpg";
        System.out.println("file path:" + path);
        File targetFile = new File(path, fileName);
        if (!targetFile.exists()) {
            //创建目录
            targetFile.mkdirs();
        }
        try {
            file.transferTo(targetFile);
        } catch (Exception e) {
            e.printStackTrace();
        }
        model.addAttribute("fileUrl", request.getContextPath() + "/upload/" + fileName);
        return "forward:/list";
    }

/**
     * 获取上传路径上的所有文件
     *
     * @param request
     * @return
     */
    @RequestMapping("/listFile")
    public ModelAndView list(HttpServletRequest request) {
        String filePath = request.getSession().getServletContext().getRealPath("/") + "upload/";
        ModelAndView modelAndView = new ModelAndView();
        File uploadDest = new File(filePath);
        String[] fileNames = uploadDest.list();
//        for (int i = 0; i < fileNames.length; i++) {
//            //输出所有文件名
//            System.out.println(fileNames[i]);
//        }
        String jsonString = JSON.toJSONString(fileNames);
        modelAndView.addObject("fileNamesJsonString", jsonString);
        System.out.println(jsonString);
        modelAndView.setViewName("listFile");
        return modelAndView;
    }

/**
 * download File
 *
 * @param request
 * @param fileName
 * @return
 * @throws IOException
 */
@RequestMapping("/download")
public ResponseEntity<byte[]> download(HttpServletRequest request, @RequestParam("fileName") String fileName) throws IOException {
    String path = request.getServletContext().getRealPath("/upload/");
    File dwFile = new File(path + File.separator + fileName);
    HttpHeaders headers = new HttpHeaders();
    //下载显示的中文名，解决中文名称乱码问题
    String downloadFileName = new String(fileName.getBytes("UTF-8"), "ISO-8859-1");
    //application/octet-stream:二进制流数据
    headers.setContentDispositionFormData("attachment", downloadFileName);
    headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
    return new ResponseEntity<byte[]>(FileUtils.readFileToByteArray(dwFile), headers, HttpStatus.CREATED);
}