谁能解释一下Spring的Multipartfile如何工作？

Question

  

我一直在尝试了解multipartfile在春季如何工作   但没有在互联网上找到任何有用的信息。

试图了解这种方法：

 public String copyUploadedImage(MultipartFile multipartFile, String realpath, int userId) throws IOException {
        String orgFileName = null;
        orgFileName = multipartFile.getOriginalFilename();
        String fileName = null;
        InputStream inputStream = null;
        OutputStream outputStream = null;
        if (multipartFile.getSize() > 0) {
            inputStream = multipartFile.getInputStream();
            String root = realpath + File.separator + userId + File.separator + "Image" + File.separator;
            File file = new File(root + File.separator);
            if (file.mkdirs()) {
                System.out.println("Directory is created!");
            } else {
                System.out.println("Failed to create directory!");
            }
            fileName = file + File.separator + multipartFile.getOriginalFilename();
            outputStream = new FileOutputStream(fileName);
            int readBytes = 0;
            byte[] buffer = new byte[10000];
            while ((readBytes = inputStream.read(buffer, 0, 10000)) != -1) {

                outputStream.write(buffer, 0, readBytes);
            }
            outputStream.flush();
            outputStream.close();
            inputStream.close();
        }
        return orgFileName;
    }