代码如下：

 @PostMapping("/upload")
    public ResponseEntity<String> handleFileUpload(@RequestParam(value = "uploadDirectory") String uploadDirectory,
                                                   @RequestParam("fileName") MultipartFile fileName) {
        try {
            // 确保文件不为空
            if (fileName.isEmpty()) {
                return ResponseEntity.badRequest().body("No file selected to upload.");
            }

            String fileNameToSave =  fileName.getOriginalFilename();

            // 构建保存文件的完整路径
            Path destinationFilePath = Paths.get(uploadDirectory, fileNameToSave);

            // 创建目录（如果不存在）
            Files.createDirectories(destinationFilePath.getParent());

            // 保存文件到指定目录
            Files.copy(fileName.getInputStream(), destinationFilePath, StandardCopyOption.REPLACE_EXISTING);

            return ResponseEntity.ok("File uploaded successfully to: " + destinationFilePath.toAbsolutePath());
        } catch (IOException ex) {
            throw new MultipartException("Could not save file.", ex);
        }
    }