1.現象是在spring-boot里加入commons-fileupload jar並且配置了mutilPart的bean，在upload的POST請求後，發現multipartRequest.getFiles=null，有點奇怪，查了文件資料才解決。

2.原因是：spring-boot自帶的和Multipart產生衝突，如果同時使用了MultipartResolver 和ServletFileUpload，就會在iter.hasNext()返回false.然後整個迴圈就跳出去了。整個問題產生的原因是Spring框架先呼叫了MultipartResolver 來處理http multi-part的請求

3、單檔案的話只需要一個變數即，多檔案上傳的話就將MultipartFile改為陣列，然後分別上傳儲存即可。

@RequestMapping(value="/multipleSave", method=RequestMethod.POST )
    public @ResponseBody String multipleSave(@RequestParam
 
("file") MultipartFile[] files){
        String fileName = null;
        String msg = "";
        if (files != null && files.length >0) {
            for(int i =0 ;i< files.length; i++){
                try {
                    fileName = files[i].getOriginalFilename();
                    byte
 
[] bytes = files[i].getBytes();
                    BufferedOutputStream buffStream = 
                            new BufferedOutputStream(new FileOutputStream(new File("/tmp/" + fileName)));
                    buffStream.write(bytes);
                    buffStream.close();
                    msg += "You have successfully uploaded " + fileName";
                } catch (Exception e) {
                    return "You failed to upload " + fileName + ": " + e.getMessage();
                }
            }
            return msg;
        } else {
            return "Unable to upload. File is empty.";
        }
    }
}

4.spring-boot 配置上傳檔案和請求檔案的最大值限制：

直接在application.properties中

multipart.maxFileSize=128KB

multipart.maxRequestSize=128KB

5、 spring-boot-starter-webare already added as dependencies. To upload files with Servlet containers, you need to register aMultipartConfigElemen class (which would be multipart-config in
web.xml). Thanks to Spring Boot, everything is auto-configured for you!