文件下载的几种方式

1.IO流方式下载(如果出现异常，返回值设为空就行了)

 @ResponseBody
    @RequestMapping(value = "/dodown",method = RequestMethod.GET)
        public HttpServletResponse download(String path, HttpServletResponse response) {
            try {
                // path是指欲下载的文件的路径。
                path = "d://upload/dtos1.jpg";
                File file = new File(path);
                // 取得文件名。
                String filename = file.getName();
                // 取得文件的后缀名。
                String ext = filename.substring(filename.lastIndexOf(".") + 1).toUpperCase();

                // 以流的形式下载文件。
                InputStream fis = new BufferedInputStream(new FileInputStream(path));
                byte[] buffer = new byte[fis.available()];
                fis.read(buffer);
                fis.close();
                // 清空response
                response.reset();
                // 设置response的Header
                response.addHeader("Content-Disposition", "attachment;filename=" + new String(filename.getBytes()));
                response.addHeader("Content-Length", "" + file.length());
                OutputStream toClient = new BufferedOutputStream(response.getOutputStream());
                response.setContentType("application/octet-stream");
                toClient.write(buffer);
                toClient.flush();
                toClient.close();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
            return response;
        }

2.下载本地文件

@ResponseBody
    @RequestMapping(value = "/dodown1",method = RequestMethod.GET)
    public void downloadLocal(HttpServletResponse response) throws FileNotFoundException {
        // 下载本地文件
        String fileName = "dtos1.jpg".toString(); // 文件的默认保存名
        // 读到流中
        InputStream inStream = new FileInputStream("d://upload/dtos1.jpg");// 文件的存放路径
        // 设置输出的格式
        response.reset();
        response.setContentType("bin");
        response.addHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");
        // 循环取出流中的数据
        byte[] b = new byte[100];
        int len;
        try {
            while ((len = inStream.read(b)) > 0)
                response.getOutputStream().write(b, 0, len);
            inStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

3.在线打开文件

@ResponseBody
    @RequestMapping(value = "/dodown3",method = RequestMethod.GET)
    public void downLoad(String filePath, HttpServletResponse response, boolean isOnLine) throws Exception {
        filePath = "d://upload/a.jpg";
        isOnLine = true;
        File f = new File(filePath);
        if (!f.exists()) {
            response.sendError(404, "File not found!");
            return;
        }
        BufferedInputStream br = new BufferedInputStream(new FileInputStream(f));
        byte[] buf = new byte[1024];
        int len = 0;

        response.reset(); // 非常重要
        if (isOnLine) { // 在线打开方式
            URL u = new URL("file:///" + filePath);
            response.setContentType(u.openConnection().getContentType());
            response.setHeader("Content-Disposition", "inline; filename=" + f.getName());
            // 文件名应该编码成UTF-8
        } else { // 纯下载方式
            response.setContentType("application/x-msdownload");
            response.setHeader("Content-Disposition", "attachment; filename=" + f.getName());
        }
        OutputStream out = response.getOutputStream();
        while ((len = br.read(buf)) > 0)
            out.write(buf, 0, len);
        br.close();
        out.close();
    }

4.下载网络文件

@ResponseBody
    @RequestMapping(value = "/dodown2",method = RequestMethod.GET)
    public void downloadNet(HttpServletResponse response) throws MalformedURLException {
        // 下载网络文件
        int bytesum = 0;
        int byteread = 0;

        URL url = new URL("http://pic.netbian.com/uploads/allimg/190824/205524-15666513248366.jpg");

        try {
            URLConnection conn = url.openConnection();
            InputStream inStream = conn.getInputStream();
            File file = new File("d://upload/a.jpg");
            FileOutputStream fs = new FileOutputStream(file);

            byte[] buffer = new byte[1204];
            int length;
            while ((byteread = inStream.read(buffer)) != -1) {
                bytesum += byteread;
                System.out.println(bytesum);
                fs.write(buffer, 0, byteread);
            }
            fs.flush();
            fs.close();
            inStream.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }