SpringMVC使用MultipartFile上传文件报错【org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.multipart.MultipartFile]: Specified class is an interface】

报错场景：

　　使用SpringMVC（或SSM框架）实现文件上传时报【 Failed to instantiate [org.springframework.web.multipart.MultipartFile]: Specified class is an interface】错，控制器代码：

package com.xjs.controller;

import org.apache.commons.io.FileUtils;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.multipart.MultipartFile;

import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;

/**
 * @ClassName:FileController
 * @Author:微微亮
 * @Description:
 * @Date:2020/9/23 11:37
 * @Version: 1.0
 */
@Controller
@RequestMapping("/myFile")
public class FileController {

    @RequestMapping("/add")
    public String upload(Model model, MultipartFile xjs) throws IOException {
        //获取文件的名字
        String filename = xjs.getOriginalFilename();
        String newFileName = System.currentTimeMillis()+filename;
        File file1 = new File("E:\myImg\"+newFileName);

        model.addAttribute("newFileName",newFileName);
        //把文件写入相应的文件夹
        xjs.transferTo(file1);
        return "forward:/show.jsp";
    }

}

解决方法：

在参数MultipartFile前加注解@RequestParam

package com.xjs.controller;

import org.apache.commons.io.FileUtils;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.multipart.MultipartFile;

import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;

/**
 * @ClassName:FileController
 * @Author:微微亮
 * @Description:
 * @Date:2020/9/23 11:37
 * @Version: 1.0
 */
@Controller
@RequestMapping("/myFile")
public class FileController {

    @RequestMapping("/add")
    public String upload(Model model, @RequestParam("xjs")MultipartFile xjs) throws IOException {
        //获取文件的名字
        String filename = xjs.getOriginalFilename();
        String newFileName = System.currentTimeMillis()+filename;
        File file1 = new File("E:\myImg\"+newFileName);

        model.addAttribute("newFileName",newFileName);
        //把文件写入相应的文件夹
        xjs.transferTo(file1);
        return "forward:/show.jsp";
    }
}

---

另一种原因是：

springMVC的配置文件中开启注解：<mvc:annotation-driven/>

可以解决上述报错

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

    <!--扫描注解-->
    <context:component-scan base-package="com.xjs"/>

    <!--开启注解-->
    <mvc:annotation-driven/>

    <!--bean支持文件上传-->
    <!--支持文件上传的bean的id是固定的，底层spring会根据这个id值来获取对象-->
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <!--设置文件上传的大小，value值的单位是B
                      默认不能超过2M
                -->
        <property name="maxUploadSize" value="10485760"></property>
    </bean>

</beans>