文件上传与下载

1. 导包

   <!-- https://mvnrepository.com/artifact/commons-fileupload/commons-fileupload -->
   <dependency>
       <groupId>commons-fileupload</groupId>
       <artifactId>commons-fileupload</artifactId>
       <version>1.4</version>
   </dependency>

2. 配置

   <!--文件上传配置-->
   <bean id="multipartResolver"  class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
       <!-- 请求的编码格式，必须和jSP的pageEncoding属性一致，以便正确读取表单的内容，默认为ISO-8859-1 -->
       <property name="defaultEncoding" value="utf-8"/>
       <!-- 上传文件大小上限，单位为字节（10485760=10M） -->
       <property name="maxUploadSize" value="10485760"/>
       <property name="maxInMemorySize" value="40960"/>
   </bean>

3. 页面

   <form action="${pageContext.request.contextPath}/upload" enctype="multipart/form-data" method="post">
       <input type="file" name="file">
    <input type="submit" name="upload" value="上传">
    <br/>
    <a href="/download">点击下载</a>
   </form>

4. 流上传

   @RequestMapping("/upload")
   public String fileUpload(@RequestParam("file") CommonsMultipartFile file , HttpServletRequest request) throws IOException {
   
       //获取文件名 : file.getOriginalFilename();
       String uploadFileName = file.getOriginalFilename();
   
       //如果文件名为空，直接回到首页！
       if ("".equals(uploadFileName)){
           return "redirect:/index.jsp";
       }
       System.out.println("上传文件名 : "+uploadFileName);
   
       //上传路径保存设置
       String path = request.getSession().getServletContext().getRealPath("/upload");
       //如果路径不存在，创建一个
       File realPath = new File(path);
       if (!realPath.exists()){
           realPath.mkdir();
       }
       System.out.println("上传文件保存地址："+realPath);
   
       InputStream is = file.getInputStream(); //文件输入流
       OutputStream os = new FileOutputStream(new File(realPath,uploadFileName)); //文件输出流
   
       //读取写出
       int len=0;
       byte[] buffer = new byte[1024];
       while ((len=is.read(buffer))!=-1){
           os.write(buffer,0,len);
           os.flush();
       }
       os.close();
       is.close();
       return "redirect:/index.jsp";
   }

   采用file.Transto 上传

   @RequestMapping("/upload2")
   public String  fileUpload2(@RequestParam("file") CommonsMultipartFile file, HttpServletRequest request) throws IOException {
   
       //上传路径保存设置
       String path = request.getSession().getServletContext().getRealPath("/upload");
       File realPath = new File(path);
       if (!realPath.exists()){
           realPath.mkdir();
       }
       //上传文件地址
       System.out.println("上传文件保存地址："+realPath);
   
       //通过CommonsMultipartFile的方法直接写文件（注意这个时候）
       file.transferTo(new File(realPath +"/"+ file.getOriginalFilename()));
   
       return "redirect:/index.jsp";
   }

5. 下载

   @RequestMapping(value="/download")
   public String downloads(HttpServletResponse response , HttpServletRequest request) throws Exception{
       //要下载的图片地址
       String  path = request.getSession().getServletContext().getRealPath("/upload");
       String  fileName = "123.jpg";
   
       //1、设置response 响应头
       response.reset(); //设置页面不缓存,清空buffer
       response.setCharacterEncoding("UTF-8"); //字符编码
       response.setContentType("multipart/form-data"); //二进制传输数据
       //设置响应头
       response.setHeader("Content-Disposition",
               "attachment;fileName="+ URLEncoder.encode(fileName, "UTF-8"));
   
       File file = new File(path,fileName);
       //2、 读取文件--输入流
       InputStream input=new FileInputStream(file);
       //3、 写出文件--输出流
       OutputStream out = response.getOutputStream();
   
       byte[] buff =new byte[1024];
       int index=0;
       //4、执行 写出操作
       while((index= input.read(buff))!= -1){
           out.write(buff, 0, index);
           out.flush();
       }
       out.close();
       input.close();
       return null;
   }

文件上传与下载

原文：https://www.cnblogs.com/pinked/p/12235288.html