Spring MVC实现文件上传和下载

<!--文件上传-->
<dependency>
 <groupId>commons-fileupload</groupId>
 <artifactId>commons-fileupload</artifactId>
 <version>1.3.3</version>
</dependency>
<!--servlet-api导入高版本的-->
<dependency>
 <groupId>javax.servlet</groupId>
 <artifactId>javax.servlet-api</artifactId>
 <version>4.0.1</version>
</dependency>

<!--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>

@RestController
public class FileController {
    //@RequestParam("file") 将name=file控件得到的文件封装成 CommonsMultipartFile 对象

    //批量上传 CommonsMultipartFile 则为数组即可
    @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.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 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();
        }
        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";
    }
}

@RequestMapping(value = "/download")
public String downloads(HttpServletResponse response, HttpServletRequest request) throws Exception {
    //要下载的图片地址
    String path = request.getServletContext().getRealPath("/upload");
    String fileName = "基础语法.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;
}