Java,MultiPart：确定上传的多部分是否是一种图像

我想创建该图像的缩略图预览,这就是我需要确定它是否是图像的原因.我有缩略图创建代码,没有什么可以知道它是否是一个图像.

请求代码 ：

@RequestMapping(value = "/notes/addattachment/{noteid}/{groupaccountid}/{api}",method = RequestMethod.POST)
    public @ResponseBody void addAttachments(@PathVariable("noteid") int noteid,@PathVariable("groupaccountid") Long groupAccountId,@PathVariable("api") String api,@RequestParam("attachments") MultipartFile attachment) {
        if (!(attachment.isEmpty())) {
            switch (api){
                case "somecase":
                    try {

                        String fileName = attachment.getOriginalFilename();
                        long fileSize = attachment.getSize();
                        byte[] bytes = attachment.getBytes();
                        this.groupAttachmentsService.addAttachment(bytes,fileName,fileSize,noteid,true,attachment.getContentType());
                        } catch (Exception ignored) {}
                    break;
                case "google":
                    this.driveQuickstart.insertFile(attachment,groupAccountId,"123");
                    break;
                case "dropbox":
                    String path = api.replace(":","/");
                    this.dropboxTask.insertFile(attachment,"path",groupAccountId);
                    break;


            }
        }
    }

你能帮忙的话,我会很高兴.谢谢.