MultipartHttpServletRequest multiRequest = (MultipartHttpServletRequest) request; // 转换成多部分request异常

原来是需要在springmvc中配置

 <!-- multipartResolver上传文件 -->
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">  
     <property name="maxUploadSize" value="104857600"/>  
       <property name="maxInMemorySize" value="4096"/>  
    </bean>