一、

1、MultipartResolver接口和文件上传下载坐标坐标

2、

案例、
结构

环境
1、pom.xml

<!--    servlet规范-->
<dependency>
  <groupId>javax.servlet</groupId>
  <artifactId>javax.servlet-api</artifactId>
  <version>3.1.0</version>
  <scope>provided</scope>
</dependency>
<!--   jsp -->
<dependency>
  <groupId>javax.servlet.jsp</groupId>
  <artifactId>jsp-api</artifactId>
  <version>2.1</version>
  <scope>provided</scope>
</dependency>

<!--      spring-->
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-webmvc</artifactId>
  <version>5.1.9.RELEASE</version>
</dependency>
<!-- spring Mvc-->
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-context</artifactId>
  <version>5.1.9.RELEASE</version>
</dependency>
<!-- spring Web-->
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-web</artifactId>
  <version>5.1.9.RELEASE</version>
</dependency>

<!--文件的上传下载-->
<dependency>
  <groupId>commons-fileupload</groupId>
  <artifactId>commons-fileupload</artifactId>
  <version>1.4</version>
</dependency>

2、spring-mvc.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">

    <!--    扫描sprig的bean-->
    <context:component-scan base-package="com.itheima"/>
    <!--    mvc驱动-->
    <mvc:annotation-driven/>
    <!--  用于上传下载的类  -->
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <!--       设置上传文件最大值-->
        <property name="maxInMemorySize" value="10240000"/>
    </bean>
</beans>

3、web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
          http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         version="3.0">
  <!--用于解决中文乱码-->
  <filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <!--拦截-->
  <servlet>
    <servlet-name>DispatcherServlet</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>
  </servlet>
  <servlet-mapping>
    <servlet-name>DispatcherServlet</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>

</web-app>

4、controller 和前端页面fileupload.jsp

5、page.jsp

6、测试

二、文件上传注意事项
1、

1.1、文件对象常用方法

案例、
1、单个文件
1.1、在webapp文件夹下创建一个images文件夹
1.2、controller层

如果request..getServletContext().getRealPath()老是输出到target目录的解决办法看：

2、多个文件
2.1、fileupload.jsp

2.2、controller层

2.3、测试

2.5、结果