ApplicationHttpRequest cannot be cast to MultipartHttpServletRequest springMVC

　　项目比较老，框架不是很灵活，遇到上传文件的问题，实验了俩个小时终于搞定。

　　1、确认<form name="contractForm" id="contractForm" action="" method="post" enctype ="multipart/form-data">；

　　2、确认commons-fileupload.jar 和 org.springframework.web.jar 存在环境

　　3、MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest)request；

　　　　这一句会报错：ApplicationHttpRequest cannot be cast to MultipartHttpServletRequest

　　那就通过这种方式：

　　MultipartResolver resolver = new CommonsMultipartResolver(request.getSession().getServletContext());

　　MultipartHttpServletRequest multipartRequest = resolver.resolveMultipart(request);