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首先jsp页面代码：

<form method="post" action="<%= request.getContextPath()%>/user/file/upload"
      enctype="multipart/form-data">
    <input type="file" name="upFile">
    <input type="submit" name="" value="上传">
</form>
<br/>
<a href="<%= request.getContextPath() %>/user/file/download?file3=a.txt">文件下载A</a>

这是一个maven项目使用spring框架：

上传下载地址：webapps下的download文件

1、依赖jar包：

第一个jar包用于文件上传处理，第二个jar包用于上传的文件输出到硬盘

	<dependency>
      <groupId>commons-fileupload</groupId>
      <artifactId>commons-fileupload</artifactId>
      <version>1.4</version>
    </dependency>

    <dependency>
      <groupId>commons-io</groupId>
      <artifactId>commons-io</artifactId>
      <version>2.4</version>
    </dependency>

2、Spring.xml文件中配置file文件处理器：

 <!--上传的文件解析器-->
    <bean id="multipartResolver"
          class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <property name="defaultEncoding" value="UTF-8"></property>
        <property name="maxInMemorySize" value="10485760"></property>
    </bean>

3、文件上传：

有三种代码，下面全部列上，任选一种即可；

Controller层代码第一种方式：

  	@RequestMapping("/file/upload")
    public void upload(MultipartFile upFile,HttpServletRequest request)  {
    
        //上传文件改名：
        
        //得到上传文件安置地址的绝对路径
        String uploadDir = request.getServletContext().getRealPath("download");
        String newFileName = UUID.randomUUID().toString();
        
        //用MultipartFile的对象方法得到文件名
        String oldFileName = upFile.getOriginalFilename();
        int index = oldFileName.lastIndexOf(".");
        String extName = oldFileName.substring(index);
        newFileName = newFileName + extName;

       //上传文件：
        FileOutputStream outputStream = null;
        try {
        //建立输出到硬盘指定目录的输出流
            outputStream = new FileOutputStream(new File(uploadDir, newFileName));
        //用commons-io   jar包里的IOUtils工具输出
            IOUtils.copy(upFile.getInputStream(), outputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                outputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

上传第二种方式：

直接用MultipartFile 对象的transfer方法。

	@RequestMapping("/file/upload")
    public void upload(MultipartFile upFile,HttpServletRequest request)  {
        //上传文件改名：
        String uploadDir = request.getServletContext().getRealPath("download");
        String newFileName = UUID.randomUUID().toString();
        String oldFileName = upFile.getOriginalFilename();
        int index = oldFileName.lastIndexOf(".");
        String extName = oldFileName.substring(index);
        newFileName = newFileName + extName;
        
      //上传文件：
      try {
            upFile.transferTo(new File(uploadDir, newFileName));
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }*/

上传代码第三种方式：

 	@RequestMapping("/file/upload")
    public void upload(MultipartFile upFile,HttpServletRequest request)  {
       InputStream inputStream =null;
        try {
            inputStream = upFile.getInputStream();
        } catch (IOException e) {
            e.printStackTrace();
        }

        //上传文件改名：
        String uploadDir = request.getServletContext().getRealPath("download");
        String newFileName = UUID.randomUUID().toString();
        String oldFileName = upFile.getOriginalFilename();
        int index = oldFileName.lastIndexOf(".");
        String extName = oldFileName.substring(index);
        newFileName = newFileName + extName;

		//上传文件：
        //用输出流把文件输出到download文件夹
        FileOutputStream outputStream = null;
        try {
            outputStream = new FileOutputStream(new File(uploadDir, newFileName));
            byte[] data = new byte[1024];
            int len = 0;
            while ((len = inputStream.read(data)) != -1) {
                outputStream.write(data,0,len);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (outputStream != null) {
                try {
                    outputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
}

4、下载文件：

 	@RequestMapping("/file/download")
    public void download(HttpServletResponse response, HttpServletRequest request) {

        //取得要下载的文件名
        String fileName = request.getParameter("file3");

        // 约定所有下载文件在服务器上的目录位置
        String download = request.getServletContext().getRealPath("download");
        File file = new File(download, fileName);

        // 处理下载
        response.setCharacterEncoding("UTF-8");
        response.setContentType("application/vnd.ms-excel");
        response.setHeader("Content-Disposition", "attachment; filename=" + fileName);
        InputStream input = null;
        OutputStream out = null;
        try {
            input = new FileInputStream(file);
            out = response.getOutputStream();
            byte[] data = new byte[1024];
            int len = 0;
            while ((len = input.read()) != -1) {
                out.write(data,0,len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if (input != null) {
                try {
                    input.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (out != null) {
                try {
                    out.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }