文件上传：CommonsMultipartResolver

一. 简介

　　CommonsMultipartResolver是基于Apache的Commons FileUpload来实现文件上传功能的,主要作用是配置文件上传的一些属性。

二. 配置　　

　　1）依赖Apache的Commons FileUpload，所以Maven的pom文件添加依赖；

<dependency>
	<groupId>commons-fileupload</groupId>
	<artifactId>commons-fileupload</artifactId>
	<version>1.3.3</version>
</dependency>

　　2）applicationContext.xml配置bean

    <!-- 文件上传解析器-->
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <property name="maxUploadSize" value="209715200"/>
        <property name="maxInMemorySize" value="40960"/>
    </bean>

　　3）id的来源，查看springMVC的核心控制器DispatcherServlet，有一些bean名字常量的定义

lic class DispatcherServlet extends FrameworkServlet {
    public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";
    public static final String LOCALE_RESOLVER_BEAN_NAME = "localeResolver";
    public static final String THEME_RESOLVER_BEAN_NAME = "themeResolver";
    public static final String HANDLER_MAPPING_BEAN_NAME = "handlerMapping";
    public static final String HANDLER_ADAPTER_BEAN_NAME = "handlerAdapter";
    public static final String HANDLER_EXCEPTION_RESOLVER_BEAN_NAME = "handlerExceptionResolver";
    public static final String REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME = "viewNameTranslator";
    public static final String VIEW_RESOLVER_BEAN_NAME = "viewResolver";
    public static final String FLASH_MAP_MANAGER_BEAN_NAME = "flashMapManager";

三. 使用

　　1）流程：

　　　　　　客户端请求必须是MultipartHttpServletRequest（HttpServletRequest的一个子类）请求 ---> spring的DispatcherServlet会调用方法checkMultipart()验证 ---> multipartResolver（会检验配置文件里面配置的一些属性：比如文件的最大值）

　　2）检验后，代码对文件的处理例子

@RequestMapping("/fileUpload")
public AjaxList fileUpload(HttpServletRequest request,HttpServletResponse response){
    MultipartHttpServletRequest multiRequest = (MultipartHttpServletRequest)request;
    MultipartFile file = multiRequest.getFile("fileName");
    if(file!=null){
        File localFile = new File("D:/"+file.getOriginalFilename());
        try {
            file.transferTo(localFile); //将上传文件写到服务器上指定的文件
        } catch (Exception e) {
            e.printStackTrace();
            return AjaxList.createError("服务器异常");
        }
    }
     return AjaxList.createSuccess("上传成功");
}