在Spring MVC的基础框架搭建起来后，我们测试了spring mvc中的返回值类型，如果你还没有搭建好springmvc的架构请参考博文->http://www.cnblogs.com/qixiaoyizhan/p/5819392.html
今天我们来讲讲spring mvc中的文件上传和下载的几种方法。
首先附上文件目录->我们需要配置的我做了记号->
一、文件上传
首先为了方便后续的操作，以及精简代码，我们在Utils包下封装一个文件上传下载的帮助类： Files_Helper_DG
Files_Helper_DG 代码
package Utils;
import org.springframework.web.multipart.MultipartFile;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.UUID;
/**
* Author:qixiao
* Time:2016-9-2 23:47:51
*/
public final class Files_Utils_DG {
/**
* private constructor method that make class can not be instantiation
*/
private Files_Utils_DG() {
throw new Error("The class Cannot be instance !");
}
/**
* spring mvc files Upload method (transferTo method)
* MultipartFile use TransferTo method upload
*
* @param request HttpServletRequest
* @param multipartFile MultipartFile(spring)
* @param filePath filePath example "/files/Upload"
* @return
*/
public static String FilesUpload_transferTo_spring(HttpServletRequest request, MultipartFile multipartFile, String filePath) {
if (multipartFile != null) {
//get files suffix
String suffix = multipartFile.getOriginalFilename().substring(multipartFile.getOriginalFilename().lastIndexOf("."));
//filePath+fileName the complex file Name
String absolutePath = getAndSetAbsolutePath(request, filePath, suffix);
//return relative Path
String relativePath = getRelativePath(filePath, suffix);
try {
//save file
multipartFile.transferTo(new File(absolutePath));
//return relative Path
return relativePath;
} catch (IOException e) {
e.printStackTrace();
return null;
}
} else
return null;
}
/**
* user stream type save files
* @param request HttpServletRequest
* @param multipartFile MultipartFile support CommonsMultipartFile file
* @param filePath filePath example "/files/Upload"
* @return
*/
public static String FilesUpload_stream(HttpServletRequest request,MultipartFile multipartFile,String filePath) {
if (multipartFile != null) {
//get files suffix
String suffix = multipartFile.getOriginalFilename().substring(multipartFile.getOriginalFilename().lastIndexOf("."));
//filePath+fileName the complex file Name
String absolutePath = getAndSetAbsolutePath(request, filePath, suffix);
//return relative Path
String relativePath = getRelativePath(filePath, suffix);
try{
InputStream inputStream = multipartFile.getInputStream();
FileOutputStream fileOutputStream = new FileOutputStream(absolutePath);
byte buffer[] = new byte[4096]; //create a buffer
long fileSize = multipartFile.getSize();
if(fileSize<=buffer.length){//if fileSize < buffer
buffer = new byte[(int)fileSize];
}
int line =0;
while((line = inputStream.read(buffer)) >0 )
{
fileOutputStream.write(buffer,0,line);
}
fileOutputStream.close();
inputStream.close();
return relativePath;
}catch (Exception e){
e.printStackTrace();
}
} else
return null;
return null;
}
/**
* @param request HttpServletRequest
* @param response HttpServletResponse
* @param filePath example "/filesOut/Download/mst.txt"
* @return
*/
public static void FilesDownload_stream(HttpServletRequest request, HttpServletResponse response, String filePath) {
//get server path (real path)
String realPath = request.getSession().getServletContext().getRealPath(filePath);
File file = new File(realPath);
String filenames = file.getName();
InputStream inputStream;
try {
inputStream = new BufferedInputStream(new FileInputStream(file));
byte[] buffer = new byte[inputStream.available()];
inputStream.read(buffer);
inputStream.close();
response.reset();
// 先去掉文件名称中的空格,然后转换编码格式为utf-8,保证不出现乱码,这个文件名称用于浏览器的下载框中自动显示的文件名
response.addHeader("Content-Disposition", "attachment;filename=" + new String(filenames.replaceAll(" ", "").getBytes("utf-8"), "iso8859-1"));
response.addHeader("Content-Length", "" + file.length());
OutputStream os = new BufferedOutputStream(response.getOutputStream());
response.setContentType("application/octet-stream");
os.write(buffer);// 输出文件
os.flush();
os.close();
} catch (Exception e) {
e.printStackTrace();
}
}
//-------------------------------------------------------------------------------
//return server absolute path（real path）
public static String getServerPath(HttpServletRequest request, String filePath) {
return request.getSession().getServletContext().getRealPath(filePath);
}
//return a dir that named date of today ; example:20160912
public static String getDataPath() {
return new SimpleDateFormat("yyyyMMdd").format(new Date());
}
//check if the path has exist if not create it
public static void checkDir(String savePath) {
File dir = new File(savePath);
if (!dir.exists() || !dir.isDirectory()) {
dir.mkdir();
}
}
//return an UUID Name parameter (suffix cover '.') example： ".jpg"、".txt"
public static String getUUIDName(String suffix) {
return UUID.randomUUID().toString() + suffix;// make new file name
}
//return server absolute path（real path） the style is “server absolute path/DataPath/UUIDName”filePath example "/files/Upload"
public static String getAndSetAbsolutePath(HttpServletRequest request, String filePath, String suffix) {
String savePath = getServerPath(request, filePath) + File.separator + getDataPath() + File.separator;//example:F:/qixiao/files/Upload/20160912/
checkDir(savePath);//check if the path has exist if not create it
return savePath + getUUIDName(suffix);
}
//get the relative path of files style is “/filePath/DataPath/UUIDName”filePath example "/files/Upload"
public static String getRelativePath(String filePath, String suffix) {
return filePath + File.separator + getDataPath() + File.separator + getUUIDName(suffix);//example:/files/Upload/20160912/
}
}
然后我们新建一个控制器类 FileUploadController
首先我们先展示出全部的代码，然后我们进行分步说明--->
package HelloSpringMVC.controller;
import Utils.Files_Utils_DG;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.multipart.MultipartHttpServletRequest;
import org.springframework.web.multipart.commons.CommonsMultipartResolver;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.Iterator;
/**
* Created by qixiao on 2016/8/30.
*/
@Controller
@RequestMapping(value = "/FileUpload/*")
public class FileUploadController {
/*
* 方式一
* 采用 fileUpload_multipartFile ， file.transferTo 来保存上传的文件
*/
@RequestMapping(value = "fileUpload_multipartFile")
@ResponseBody
public String fileUpload_multipartFile(HttpServletRequest request, @RequestParam("file_upload") MultipartFile multipartFile) {
//调用保存文件的帮助类进行保存文件，并返回文件的相对路径
String filePath = Files_Utils_DG.FilesUpload_transferTo_spring(request, multipartFile, "/files/upload");
return "{'TFMark':'true','Msg':'upload success !','filePath':'" + filePath + "'}";
}
/*
* 方式二
* 采用 fileUpload_multipartRequest file.transferTo 来保存上传文件
* 参数不写 MultipartFile multipartFile 在request请求里面直接转成multipartRequest，从multipartRequest中获取到文件流
*/
@RequestMapping(value = "fileUpload_multipartRequest")
@ResponseBody
public String fileUpload_multipartRequest(HttpServletRequest request) {
//将request转成MultipartHttpServletRequest
MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest) request;
//页面控件的文件流，对应页面控件 input file_upload
MultipartFile multipartFile = multipartRequest.getFile("file_upload");
//调用保存文件的帮助类进行保存文件，并返回文件的相对路径
String filePath = Files_Utils_DG.FilesUpload_transferTo_spring(request, multipartFile, "/files/upload");
return "{'TFMark':'true','Msg':'upload success !','filePath':'" + filePath + "'}";
}
/*
* 方式三
* 采用 CommonsMultipartResolver file.transferTo 来保存上传文件
* 自动扫描全部的input表单
*/
@RequestMapping(value = "fileUpload_CommonsMultipartResolver")
@ResponseBody
public String fileUpload_CommonsMultipartResolver(HttpServletRequest request) {
//将当前上下文初始化给 CommonsMultipartResolver （多部分解析器）
CommonsMultipartResolver multipartResolver = new CommonsMultipartResolver(request.getSession().getServletContext());
//检查form中是否有enctype="multipart/form-data"
if (multipartResolver.isMultipart(request)) {
//将request变成多部分request
MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest) request;
//获取multiRequest 中所有的文件名
Iterator iter = multipartRequest.getFileNames();
while (iter.hasNext()) {
//一次遍历所有文件
MultipartFile multipartFile = multipartRequest.getFile(iter.next().toString());
//调用保存文件的帮助类进行保存文件，并返回文件的相对路径
String fileName = Files_Utils_DG.FilesUpload_transferTo_spring(request, multipartFile, "/files/upload");
System.out.println(fileName);
}
}
return "upload success ! ";
}
/*
* 方式四
* 通过流的方式上传文件
*/
@RequestMapping("fileUpload_stream")
@ResponseBody
public String upFile(HttpServletRequest request, @RequestParam("file_upload") MultipartFile multipartFile){
String filePath= Files_Utils_DG.FilesUpload_stream(request,multipartFile,"/files/upload");
return "{'TFMark':'true','Msg':'upload success !','filePath':'" + filePath + "'}";
}
/*
* 方式五
* 采用 fileUpload_ajax ， file.transferTo 来保存上传的文件 异步
*/
@RequestMapping(value = "fileUpload_ajax",method = RequestMethod.POST,produces = {"application/json;charset=UTF-8"})
@ResponseBody
public String fileUpload_ajax(HttpServletRequest request, @RequestParam("file_AjaxFile") MultipartFile multipartFile) {
//调用保存文件的帮助类进行保存文件，并返回文件的相对路径
String filePath = Files_Utils_DG.FilesUpload_transferTo_spring(request, multipartFile, "/files/upload");
return "{'TFMark':'true','Msg':'upload success !','filePath':'" + filePath + "'}";
}
/*
* 多文件上传
* 采用 MultipartFile[] multipartFile 上传文件方法
*/
@RequestMapping(value = "fileUpload_spring_list")
@ResponseBody
public String fileUpload_spring_list(HttpServletRequest request, @RequestParam("file_upload") MultipartFile[] multipartFile) {
//判断file数组不能为空并且长度大于0
if (multipartFile != null && multipartFile.length > 0) {
//循环获取file数组中得文件
try {
for (int i = 0; i < multipartFile.length; i++) {
MultipartFile file = multipartFile[i];
//保存文件
String fileName = Files_Utils_DG.FilesUpload_transferTo_spring(request, file, "/files/upload");
System.out.println(fileName);
}
return "{'TFMark':'true','Msg':'upload success !'}";
} catch (Exception ee) {
return "{'TFMark':'false','Msg':'参数传递有误！'}";
}
}
return "{'TFMark':'false','Msg':'参数传递有误！'}";
}
/**
* 文件下载
*
* @param response
*/
@RequestMapping(value = "fileDownload_servlet")
public void fileDownload_servlet(HttpServletRequest request, HttpServletResponse response) {
Files_Utils_DG.FilesDownload_stream(request,response,"/files/download/mst.txt");
}
}
方式一：采用 fileUpload_multipartFile ， file.transferTo 来保存上传的文件
/*
* 方式一
* 采用 fileUpload_multipartFile ， file.transferTo 来保存上传的文件
*/
@RequestMapping(value = "fileUpload_multipartFile")
@ResponseBody
public String fileUpload_multipartFile(HttpServletRequest request, @RequestParam("file_upload") MultipartFile multipartFile) {
//调用保存文件的帮助类进行保存文件，并返回文件的相对路径
String filePath = Files_Helper_DG.FilesUpload_transferTo_spring(request, multipartFile, "/filesOut/Upload");
return "{\"TFMark\":\"true\",\"Msg\":\"upload success !\",\"filePath\":\"" + filePath + "\"}";
}
方式二：采用 fileUpload_multipartRequest file.transferTo 来保存上传文件
@RequestMapping(value = "fileUpload_multipartRequest")
@ResponseBody
public String fileUpload_multipartRequest(HttpServletRequest request) {
//将request转成MultipartHttpServletRequest
MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest) request;
//页面控件的文件流，对应页面控件 input file_upload
MultipartFile multipartFile = multipartRequest.getFile("file_upload");
//调用保存文件的帮助类进行保存文件，并返回文件的相对路径
String filePath = Files_Helper_DG.FilesUpload_transferTo_spring(request, multipartFile, "/filesOut/Upload");
return "{\"TFMark\":\"true\",\"Msg\":\"upload success !\",\"filePath\":\"" + filePath + "\"}";
}
方式三：采用 CommonsMultipartResolver file.transferTo 来保存上传文件---自动扫描全部的input表单
@RequestMapping(value = "fileUpload_CommonsMultipartResolver")
@ResponseBody
public String fileUpload_CommonsMultipartResolver(HttpServletRequest request) {
//将当前上下文初始化给 CommonsMultipartResolver （多部分解析器）
CommonsMultipartResolver multipartResolver = new CommonsMultipartResolver(request.getSession().getServletContext());
//检查form中是否有enctype="multipart/form-data"
if (multipartResolver.isMultipart(request)) {
//将request变成多部分request
MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest) request;
//获取multiRequest 中所有的文件名
Iterator iter = multipartRequest.getFileNames();
while (iter.hasNext()) {
//一次遍历所有文件
MultipartFile multipartFile = multipartRequest.getFile(iter.next().toString());
//调用保存文件的帮助类进行保存文件，并返回文件的相对路径
String fileName = Files_Helper_DG.FilesUpload_transferTo_spring(request, multipartFile, "/filesOut/Upload");
System.out.println(fileName);
}
}
return "upload success ! ";
}
方式四：通过流的方式上传文件
@RequestMapping("fileUpload_stream")
@ResponseBody
public String upFile(HttpServletRequest request, @RequestParam("file_upload") MultipartFile multipartFile){
String filePath=Files_Helper_DG.FilesUpload_stream(request,multipartFile,"/filesOut/Upload");
return "{\"TFMark\":\"true\",\"Msg\":\"upload success !\",\"filePath\":\"" + filePath + "\"}";
}
方式五：采用ajaxFileUpload.js插件与异步上传的方式上传文件
@RequestMapping(value = "fileUpload_ajax",method = RequestMethod.POST,produces = {"application/json;charset=UTF-8"})
@ResponseBody
public String fileUpload_ajax(HttpServletRequest request, @RequestParam("file_AjaxFile") MultipartFile multipartFile) {
//调用保存文件的帮助类进行保存文件，并返回文件的相对路径
String filePath = Files_Utils_DG.FilesUpload_transferTo_spring(request, multipartFile, "/files/upload");
return "{'TFMark':'true','Msg':'upload success !','filePath':'" + filePath + "'}";
}
上述方法需要 ajaxfileupload.js 插件的支持,该插件
多文件上传（其实是将上面的 MultipartFile 写成数组形式）
@RequestMapping(value = "fileUpload_spring_list")
@ResponseBody
public String fileUpload_spring_list(HttpServletRequest request, @RequestParam("file_upload") MultipartFile[] multipartFile) {
//判断file数组不能为空并且长度大于0
if (multipartFile != null && multipartFile.length > 0) {
//循环获取file数组中得文件
try {
for (int i = 0; i < multipartFile.length; i++) {
MultipartFile file = multipartFile[i];
//保存文件
String fileName = Files_Helper_DG.FilesUpload_transferTo_spring(request, file, "/filesOut/Upload");
System.out.println(fileName);
}
return "{\"TFMark\":\"true\",\"Msg\":\"upload success !\"}";
} catch (Exception ee) {
return "{\"TFMark\":\"false\",\"Msg\":\"参数传递有误！\"}";
}
}
return "{\"TFMark\":\"false\",\"Msg\":\"参数传递有误！\"}";
}
下面我们进行测试：
首先在webapp下新建文件夹目录/files/download，并且新建一个/Views/FileUpload/FileUpload.jsp
注意文件目录结构以及目录层次！！！
FileUpload.jsp代码如下
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";
%>
<html>
<head>
<base href="<%=basePath%>">
<title>fileUpload</title>
<script src="<%=basePath%>scripts/jquery-1.11.1.js"></script>
<script src="<%=basePath%>scripts/ajaxfileupload.js"></script>
</head>
<body>
<h3>文件上传</h3><br>
<h3>采用 fileUpload_multipartFile ， file.transferTo 来保存上传的文件</h3>
<form name="form1" action="/FileUpload/fileUpload_multipartFile" method="post" enctype="multipart/form-data">
<input type="file" name="file_upload">
<input type="submit" value="upload"/>
</form>
<hr>
<h3>采用 fileUpload_multipartRequest file.transferTo 来保存上传文件</h3>
<form name="form2" action="/FileUpload/fileUpload_multipartRequest" method="post" enctype="multipart/form-data">
<input type="file" name="file_upload">
<input type="submit" value="upload"/>
</form>
<hr>
<h3>采用 CommonsMultipartResolver file.transferTo 来保存上传文件</h3>
<form name="form3" action="/FileUpload/fileUpload_CommonsMultipartResolver" method="post" enctype="multipart/form-data">
<input type="file" name="file_upload">
<input type="submit" value="upload"/>
</form>
<hr>
<h3>通过流的方式上传文件</h3>
<form name="form4" action="/FileUpload/fileUpload_stream" method="post" enctype="multipart/form-data">
<input type="file" name="file_upload">
<input type="submit" value="upload"/>
</form>
<hr>
<h3>通过ajax插件 ajaxfileupload.js 来异步上传文件</h3>
<form name="form5" action="/" method="post" enctype="multipart/form-data">
<input type="file" id="file_AjaxFile" name="file_AjaxFile">
<input type="button" value="upload" onclick="fileUploadAjax()"/><span id="sp_AjaxFile"></span><br><br>
上传进度：<span id="sp_fileUploadProgress">0%</span>
</form>
<script type="text/javascript">
function fileUploadAjax() {
if ($("#file_AjaxFile").val().length > 0) {
progressInterval=setInterval(getProgress,500);
$.ajaxFileUpload({
url: '/FileUpload/fileUpload_ajax', //用于文件上传的服务器端请求地址
type: "post",
secureuri: false, //一般设置为false
fileElementId: 'file_AjaxFile', //文件上传空间的id属性 <input type="file" id="file1" name="file" />
dataType: 'application/json', //返回值类型 一般设置为json
success: function (data) //服务器成功响应处理函数
{
var jsonObject = eval('(' + data + ')');
$("#sp_AjaxFile").html(" Upload Success ！ filePath:" + jsonObject.filePath);
},
error: function (data, status, e)//服务器响应失败处理函数
{
alert(e);
}
});//end ajaxfile
}
else {
alert("请选择文件!");
}
}
var progressInterval = null;
var i=0;
var getProgress=function (){
$.get("/FileUpload/fileUploadprogress",
{},
function (data) {
$("#sp_fileUploadProgress").html(i+++data);
if(data==100||i==100)
clearInterval(progressInterval);
}
);
}
</script>
<hr>
<h3>多文件上传 采用 MultipartFile[] multipartFile 上传文件方法</h3>
<form name="form5" action="/FileUpload/fileUpload_spring_list" method="post" enctype="multipart/form-data">
<input type="file" name="file_upload">
<input type="file" name="file_upload">
<input type="file" name="file_upload">
<input type="submit" value="upload"/>
</form>
<hr>
<h3>通过 a 标签的方式进行文件下载</h3><br>
<a href="<%=basePath%>filesOut/Download/mst.txt">通过 a 标签下载文件 mst.txt</a>
<hr>
<h3>通过 Response 文件流的方式下载文件</h3>
<a href="/FileUpload/fileDownload_servlet">通过 文件流 的方式下载文件 mst.txt</a>
</body>
</html>
这里一定要记得在spring-servlet.xml里面配置访问静态路径方法->下面我附上spring-servlet.xml
<?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-3.1.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.1.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd">
<!-- 启动注解驱动的Spring MVC功能，注册请求url和注解POJO类方法的映射-->
<mvc:annotation-driven >
</mvc:annotation-driven>
<!-- 启动包扫描功能，以便注册带有@Controller、@service、@repository、@Component等注解的类成为spring的bean -->
<context:component-scan base-package="HelloSpringMVC.controller" />
<!-- 对模型视图名称的解析，在请求时模型视图名称添加前后缀 -->
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
<property name="prefix" value="/"/> <!-- 前缀 -->
<property name="suffix" value=".jsp"/> <!-- 后缀 -->
</bean>
<!-- 访问静态文件（jpg,js,css）的方法 -->
<mvc:resources location="/files/" mapping="/files/**" />
<mvc:resources location="/scripts/" mapping="/scripts/**" />
<mvc:resources location="/styles/" mapping="/styles/**" />
<mvc:resources location="/Views/" mapping="/Views/**" />
<!-- 多部分文件上传 需配置MultipartResolver处理器-->
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
<property name="maxUploadSize" value="104857600" />
<property name="maxInMemorySize" value="4096" />
<property name="defaultEncoding" value="UTF-8"></property>
</bean>
<!-- SpringMVC在超出上传文件限制时,会抛出org.springframework.web.multipart.MaxUploadSizeExceededException -->
<!-- 该异常是SpringMVC在检查上传的文件信息时抛出来的,而且此时还没有进入到Controller方法中 -->
<bean id="exceptionResolver" class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
<property name="exceptionMappings">
<props>
<!-- 遇到MaxUploadSizeExceededException异常时,自动跳转到/WEB-INF/jsp/error_fileupload.jsp页面 -->
<prop key="org.springframework.web.multipart.MaxUploadSizeExceededException">error_fileupload</prop>
</props>
</property>
</bean>
</beans>
然后我们运行tomcat进入http://localhost:8080/Views/FileUpload/FileUpload.jsp
打开后，页面如下：
我们依次选择文件->
共八个文件！
然后依次点击upload按钮，进行文件的上传->
可见，六种上传都已经执行成功！下面我们打开文件目录查看一下上传的文件->
一共八个文件！证明所有文件都上传成功了！
二、文件下载
在控制器类 FileUploadController里面继续添加代码->
@RequestMapping(value = "fileDownload_servlet")
public void fileDownload_servlet(HttpServletRequest request, HttpServletResponse response) {
Files_Helper_DG.FilesDownload_servlet(request,response,"/filesOut/Download/mst.txt");
}
这里调用了帮助类 Files_Helper_DG.FilesDownload_servlet(request,response,"/filesOut/Download/mst.txt");
然后我们进行测试->
前面我们新建的文件夹/files/download，在里面放一个文件mst.txt,代码访问的就是这个文件！
然后是我们FileUpload.jsp,前面已经拷贝过了这段代码->
<h3>通过 a 标签的方式进行文件下载</h3><br> <a href="<%=basePath%>filesOut/Download/mst.txt">通过 a 标签下载文件 mst.txt</a> <hr> <h3>通过 Response 文件流的方式下载文件</h3> <a href="/FileUpload/fileDownload_servlet">通过 文件流 的方式下载文件 mst.txt</a>
首先是第一种直接访问文件目录，此方式有缺陷，暴露了项目文件结构，造成安全隐患！
点击便可下载！（如果浏览器可以读取文件，则会直接浏览器打开，我们可以右键->链接另存为选择路径保存）
然后我们点击第二种下载方式->实际项目中，我们应该优先选择第二种方式，提高了安全性！
从服务器直接下载到浏览器默认的保存文件目录！（本人在F:）
到此，我们的 spring mvc 文件上传下载已经实现！
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