文件上传下载

导包

<dependencies>
    <dependency>
        <groupId>commons-fileupload</groupId>
        <artifactId>commons-fileupload</artifactId>
        <version>1.3.3</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>4.0.1</version>
    </dependency>
</dependencies>

文件上传配置

spring-mvc.xml

<!--文件上传配置-->
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
    <!--请求得编码个,必须和jsp得pageEncoding属性一致,以便正确读取表单的内容,默认 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>

上传-前端

<form action="${pageContext.request.contextPath}/upload2" enctype="multipart/form-data" method="post">
  <input type="file" name="file">
  <input type="submit">
</form>

上传-后端

@Controller
public class FileController {
    // @RequestParam("file") 将name=file控件得到的文件封装为CommonsMultipartResolver对象
    // 批量上传CommonsMultipartResolver则为数组即可
    @RequestMapping("/upload")
    public String upload(@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,直接返回到首页!
        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.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();
        FileOutputStream os = new FileOutputStream(new File(realPath, uploadFileName));

        // 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.Tranto 来保存上传的文件
     */
    @RequestMapping("/upload2")
    public String fileUpload2(@RequestParam("file") CommonsMultipartFile file, HttpServletRequest request) throws IOException {
        // 上传路径保存设置
        String path = request.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";
    }
}

文件下载-后端

    @RequestMapping("/download")
    public String downloads(HttpServletResponse response, HttpServletRequest request) throws IOException {
        // 要下载的图片地址
        String path = request.getServletContext().getRealPath("/upload");
        String fileName = "2019年公务员多省联考《申论》题（天津卷）.pdf";

        // 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
        response.setHeader("Content-Disposition", "attachment;fileName=" + URLEncoder.encode(fileName, "UTF-8"));

        // 2.读取文件
        File file = new File(path, fileName);
        FileInputStream input = new FileInputStream(file);

        // 3.写出文件
        ServletOutputStream out = response.getOutputStream();

        byte[] buff = new byte[1024];
        int index = 0;
        while ((index = input.read(buff)) != -1) {
            out.write(buff, 0, index);
            out.flush();
        }
        out.close();
        input.close();
        return null;
    }