Spring MVC 实现文件的上传和下载

<?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">

    <context:component-scan base-package="edu.nf.ch08.controller"/>

    <mvc:annotation-driven/>

    <mvc:default-servlet-handler/>
    <!-- 文件上传有两种方式，一种基于Servlet3.0的上传，一种基于
     commons-upload上传，如果使用Servlet3.0的上传方式，可以
     不需要配置MultipartResolver，Spring默认会注册一个
     StandardServletMultipartResolver。只需要在web.xml中
     启用<multipart-config>。
     如果想使用commons-upload，那么需要配置一个CommonsMultipartResolver,
     且指定bean的id为multipartResolver-->
    <!-- 这里使用commons-upload-->
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <!-- 限制文件上传的总大小（单位：字节）,不配置此属性默认不限制 -->
        <property name="maxUploadSize" value="104857600"/>
        <!-- 设置文件上传的默认编码-->
        <property name="defaultEncoding" value="utf-8"/>
    </bean>

    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
</beans>

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <!-- 请求总控器 -->
    <servlet>
        <servlet-name>dispatcher</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:dispatcher-servlet.xml</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>dispatcher</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

</web-app>

package edu.nf.ch08.controller;

import org.apache.commons.io.FileUtils;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.servlet.ModelAndView;

import java.io.File;
import java.io.IOException;

/**
 * @author wangl
 * @date 2018/11/2
 */
@Controller
public class UploadController {

    /**
     * 文件上传只需要Spring传入一个MultipartFile对象即可，
     * 这个对象可以获取文件相关上传的信息。
     * 一个MultipartFile表示单个文件上传，当需要上传多个文件时
     * 只需要声明为MultipartFile[]数组即可。
     * @return
     */
    @PostMapping("/upload")
    public ModelAndView upload(MultipartFile file){
        //获取当前系统用户目录
        String home = System.getProperty("user.home");
        //指定上传的文件夹目录
        File uploadDir = new File(home + "/files");
        //如果目录不存在，则创建
        if(!uploadDir.exists()){
            uploadDir.mkdir();
        }
        //获取上传的文件名
        String fileName = file.getOriginalFilename();
        //构建一个完整的文件上传对象
        File uploadFile = new File(uploadDir.getAbsolutePath() + "/" + fileName);
        try {
            //通过transferTo方法进行上传
            file.transferTo(uploadFile);
        } catch (IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e.getMessage());
        }
        //将文件名存入Model，转发到index页面
        ModelAndView mv = new ModelAndView("index");
        mv.addObject("fileName", fileName);
        return mv;
    }

    /**
     * 文件下载
     * 读取服务器本地文件并封装为ResponseEntity对象
     * 响应客户端,写回的是一个字节数组
     * @param fileName 文件名
     * @return
     */
    @GetMapping("/download")
    public ResponseEntity<byte[]> download(String fileName){
        //依据文件名构建本地文件路径
        String filePath = System.getProperty("user.home") + "/files/" + fileName;
        //依据文件路径构建File对象
        File file = new File(filePath);
        //创建响应头对象，设置响应信息
        HttpHeaders headers = new HttpHeaders();
        try {
            //对文件名进行重新编码，防止在响应头中出现中文乱码
            String headerFileName = new String(fileName.getBytes("UTF-8"), "ISO-8859-1");
            //设置响应内容处理方式为附件,并指定文件名
            headers.setContentDispositionFormData("attachment", headerFileName);
            //设置响应头类型为application/octet-stream,表示是一个流类型
            headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
            //将文件转换成字节数组
            byte[] bytes = FileUtils.readFileToByteArray(file);
            //创建ResponseEntity对象（封装文件字节数组、响应头、响应状态码）
            ResponseEntity<byte[]> entity = new ResponseEntity<>(bytes, headers, HttpStatus.CREATED);
            //最后将整个ResponseEntity对象返回给DispatcherServlet
            return entity;
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException("文件下载失败");
        }
    }
}

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h1>文件上传</h1>
<!-- 当有文件上传时，表单的enctype必须设置为multipart/form-data -->
<form method="post" action="upload" enctype="multipart/form-data">
    File:<input type="file" name="file"/><br/>
    <input type="submit" value="submit"/>
</form>
</body>
</html>

<%--
  Created by IntelliJ IDEA.
  User: wangl
  Date: 2018/11/2
  Time: 09:56
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<a href="download?fileName=${fileName}">${fileName}</a>
</body>
</html>