1.ajax传过去的参数在controller接受不到

解决：在contoller中增加@RequestParam

例如：saveUploadFile( @RequestParam("file") MultipartFile file,HttpServletRequest request)

2.org.springframework.web.multipart.support.MissingServletRequestPartException: Required request part 'file' is not present

将ajax 请求的contextType 改成是“multipart/form-data; charset=utf-8”，原来是“text/html; charset=UTF-8”格式都是不对的。还是会出现问题，最后改到 contentType: false，请求不使用contentType

3.org.thymeleaf.exceptions.TemplateInputException: Error resolving template "test/upload", template might not exist or might not be accessible by any of the configured Template Resolvers

解决：是contorller层没有返回数据，要么返回String 直接指向页面，要么返回数据值输出