ApplicationHttpRequest cannot be cast to MultipartHttpServletRequest springMVC 文件上傳轉換出錯解決

　　項目比較老，框架不是很靈活，遇到上傳文件的問題，實驗了倆個小時終於搞定。

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

　　2、確認commons-fileupload.jar 和 org.springframework.web.jar 存在環境

　　3、MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest)request；

　　　　這一句會報錯：ApplicationHttpRequest cannot be cast to MultipartHttpServletRequest

　　那就通過這種方式：

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

　　MultipartHttpServletRequest multipartRequest = resolver.resolveMultipart(request);