Spring MVC之MultipartResolver

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MultipartResolver是spring提供的文件上传解析器的接口，该接口有两个实现类：StandardServletMultipartResolver、CommonsMultipartResolver，MultipartResolver#isMultipart是判断是否文件上传的请求，post请求、contentType是否是以multipart/开头这两个是先决条件。

在spring上下文中，有且只有一个该实例。 spring容器启动时初始化文件上传解析器：

DispatcherServlet#initStrategies(ApplicationContext context) {
	initMultipartResolver(context);
}

• StandardServletMultipartResolver
  基于Servlet3.0 API实现，不需要引入额外的jar包，在spring的配置文件中注入此Bean时，不需要配置上传文件大小等参数，但是在web.xml中配置DispatcherServlet时，需要添加multipart-config配置。

  <servlet>
     <servlet-name>springmvc</servlet-name>
      <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
      <init-param>
          <param-name>contextConfigLocation</param-name>
          <param-value>classpath:Spring_mvc.xml</param-value>
      </init-param>
      <load-on-startup>1</load-on-startup>
      <multipart-config>
          <!--临时文件的目录-->
          <location>d:/</location>
          <!-- 上传文件的大小限制 -->
          <max-file-size>5242880</max-file-size>
          <!-- 一次表单提交中文件的大小限制 -->
          <max-request-size>10485760</max-request-size>
          <!-- 多大的文件会被自动保存到硬盘上  0：所有 -->
          <file-size-threshold>0</file-size-threshold>
      </multipart-config>
  </servlet>
  <servlet-mapping>
      <servlet-name>springmvc</servlet-name>
      <url-pattern>/</url-pattern>
  </servlet-mapping>
  

   Standard implementation of the {@link MultipartResolver} interface,
   based on the Servlet 3.0 {@link javax.servlet.http.Part} API.
   To be added as "multipartResolver" bean to a Spring DispatcherServlet context,
   without any extra configuration at the bean level (see below).
  
   <p><b>Note:</b> In order to use Servlet 3.0 based multipart parsing,
   you need to mark the affected servlet with a "multipart-config" section in
   {@code web.xml}, or with a {@link javax.servlet.MultipartConfigElement}
   in programmatic servlet registration, or (in case of a custom servlet class)
   possibly with a {@link javax.servlet.annotation.MultipartConfig} annotation
   on your servlet class. Configuration settings such as maximum sizes or
   storage locations need to be applied at that servlet registration level;
   Servlet 3.0 does not allow for them to be set at the MultipartResolver level.
  

• CommonsMultipartResolver
  基于Apache Commons FileUpload实现，继承自apache的CommonsFileUploadSupport。在spring中注入CommonsMultipartResolver时，可以配置"maxUploadSize", "maxInMemorySize" and "defaultEncoding"等属性。需要依赖jar：commons-fileupload、commons-io。

  <bean id="multipartResolver"
  		class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
  		<!-- 其他配置参见CommonsFileUploadSupport中以set开头的方法 -->
  		<property name="defaultEncoding" value="UTF-8" />
  		<property name="maxUploadSize" value="5242880" />
  		<property name="maxInMemorySize" value="40960" />
  	</bean>
  

   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).
  

在controller中用MultipartFile和MultipartHttpServletRequest接收参数即可，具体可以尝试解析这两种方式有什么API