六、SpringMVC实现文件上传下载

SpringMVC-servlet.xml

使用springMVC来处理文件上传和下载需要添加如下的配置文件，而且id是固定的
可以到org.springframework.web.servlet.DispatcherServlet的源码文件下查看
CommonsMultipartResolver提供三个属性设置，可以跳转到源码开头的注释查看
SpringMVC-servlet.xml中添加以下：

<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
       <property name="DefaultEncoding" value="UTF-8" />
       <property name="MaxUploadSize" value="1048576" />
       <property name="MaxInMemorySize" value="4096"/>  
</bean>

CommonsMultipartResolver源码注释部分片段：

/**
 * Servlet-based {@link MultipartResolver} implementation for
 * <a href="http://commons.apache.org/proper/commons-fileupload">Apache Commons FileUpload</a>
 * 1.2 or above.
 *
 * <p>Provides "maxUploadSize", "maxInMemorySize" and "defaultEncoding" settings as
 * bean properties (inherited from {@link CommonsFileUploadSupport}). See corresponding
 * ServletFileUpload / DiskFileItemFactory properties ("sizeMax", "sizeThreshold",
 * "headerEncoding") for details in terms of defaults and accepted values.
 *
 * <p>Saves temporary files to the servlet container's temporary directory.
 * Needs to be initialized <i>either</i> by an application context <i>or</i>
 * via the constructor that takes a ServletContext (for standalone usage).
 */
public class CommonsMultipartResolver extends CommonsFileUploadSupport{}

springmvc的DispatcherServlet部分源码

/** Well-known name for the MultipartResolver object in the bean factory for this namespace. */
    public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";

    /** Well-known name for the LocaleResolver object in the bean factory for this namespace. */
    public static final String LOCALE_RESOLVER_BEAN_NAME = "localeResolver";

    /** Well-known name for the ThemeResolver object in the bean factory for this namespace. */
    public static final String THEME_RESOLVER_BEAN_NAME = "themeResolver";

    /**
     * Well-known name for the HandlerMapping object in the bean factory for this namespace.
     * Only used when "detectAllHandlerMappings" is turned off.
     * @see #setDetectAllHandlerMappings
     */
    public static final String HANDLER_MAPPING_BEAN_NAME = "handlerMapping";

    /**
     * Well-known name for the HandlerAdapter object in the bean factory for this namespace.
     * Only used when "detectAllHandlerAdapters" is turned off.
     * @see #setDetectAllHandlerAdapters
     */
    public static final String HANDLER_ADAPTER_BEAN_NAME = "handlerAdapter";

    /**
     * Well-known name for the HandlerExceptionResolver object in the bean factory for this namespace.
     * Only used when "detectAllHandlerExceptionResolvers" is turned off.
     * @see #setDetectAllHandlerExceptionResolvers
     */
    public static final String HANDLER_EXCEPTION_RESOLVER_BEAN_NAME = "handlerExceptionResolver";

    /**
     * Well-known name for the RequestToViewNameTranslator object in the bean factory for this namespace.
     */
    publi