// 单文件上传
@RequestMapping(value = "/upload")
@ResponseBody
public String upload(@RequestParam("file") MultipartFile file) {
  try {
  if (file.isEmpty()) {
    return "文件为空";
  }
  // 获取文件名
  String fileName = file.getOriginalFilename();
  logger.info("上传的文件名为：" + fileName);
  // 获取文件的后缀名
  String suffixName = fileName.substring(fileName.lastIndexOf("."));
  logger.info("文件的后缀名为：" + suffixName);
  // 设置文件存储路径
  String filePath = "D://aim//";
  String path = filePath + fileName + suffixName;
  File dest = new File(path);
  // 检测是否存在目录
  if (!dest.getParentFile().exists()) {
    dest.getParentFile().mkdirs();// 新建文件夹
  }
  file.transferTo(dest);// 文件写入
  return "上传成功";
  } catch (IllegalStateException e) {
    e.printStackTrace();
  } catch (IOException e) {
    e.printStackTrace();
  }
  return "上传失败";
}

//多文件上传
@RequestMapping(value = "/uploadMore", method = RequestMethod.POST)
@ResponseBody
public String handleFileUpload(HttpServletRequest request) {
  List files = ((MultipartHttpServletRequest) request).getFiles("file");
  MultipartFile file = null;
  BufferedOutputStream stream = null;
  for (int i = 0; i < files.size(); ++i) {
    file = files.get(i);
    String filePath = "D://aim//";
    if (!file.isEmpty()) {
      try {
        byte[] bytes = file.getBytes();
        stream = new BufferedOutputStream(new FileOutputStream(
            new File(filePath + file.getOriginalFilename())));//设置文件路径及名字
        stream.write(bytes);// 写入
        stream.close();
      } catch (Exception e) {
        stream = null;
        return "第 " + i + " 个文件上传失败 ==> "
            + e.getMessage();
      }
    } else {
      return "第 " + i
          + " 个文件上传失败因为文件为空";
    }
  }
  return "上传成功";
}

//文件下载相关代码
@RequestMapping("/download")
public String downloadFile(HttpServletRequest request, HttpServletResponse response) {
  String fileName = "aim_test.txt";// 设置文件名，根据业务需要替换成要下载的文件名
  if (fileName != null) {
    //设置文件路径
    String realPath = "D://aim//"
    File file = new File(realPath , fileName);
    if (file.exists()) {
      response.setContentType("application/force-download");// 设置强制下载不打开
      response.addHeader("Content-Disposition", "attachment;fileName=" + fileName);// 设置文件名
      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;
}

@Configuration
public class MultipartConfig {
  @Bean
  public MultipartConfigElement multipartConfigElement() {
    MultipartConfigFactory factory = new MultipartConfigFactory();
    // 置文件大小限制 ,超出此大小页面会抛出异常信息
    factory.setMaxFileSize("2MB"); //KB,MB
    // 设置总上传数据总大小
    factory.setMaxRequestSize("20MB");
    // 设置文件临时文件夹路径
    // factory.setLocation("E://test//");
    // 如果文件大于这个值，将以文件的形式存储，如果小于这个值文件将存储在内存中，默认为0
    // factory.setMaxRequestSize(0);
    return factory.createMultipartConfig();
  }
}