@ReponseBody不支持form-data，所以要接收带有文件的form-data有3种方式。方式一:@PostMapping("upload")publicStringupload(MultipartFilefile,Stringusername,Stringpassword){}方式二（前端要把其他参数打包成json字符串）@PostMapping("upload")publicStringupload(MultipartFilefile,Userjson){}publicclassUser{privateStringusername;privateStringpassword}方式