// 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();
 }
}