java 下载网络文件到本地

public void downauthimg() throws MalformedURLException, IOException {

        String url = "https://picsum.photos/300/150/?image=";
        for (int i = 0; i <= 200; i++) {
            int num = 0;
            if (i == 0) {
                num = 300;
            } else {
                num = 300 + i;
            }
            String imgurl = url + num;
            try {

                // 构造URL
                URL weburl = new URL(imgurl);
                // 打开连接
                URLConnection con = weburl.openConnection();
                // 设置请求超时为5s
                con.setConnectTimeout(5 * 1000);
                // 输入流
                InputStream is = con.getInputStream();

                // 1K的数据缓冲
                byte[] bs = new byte[1024];
                // 读取到的数据长度
                int len;
                // 输出的文件流
                File sf = new File("authimg");

                if (!sf.exists()) {
                    sf.mkdirs();
                }
                OutputStream os = new FileOutputStream(sf.getPath() + "\" + i + ".jpg");
                // 开始读取
                while ((len = is.read(bs)) != -1) {
                    os.write(bs, 0, len);
                }
                // 完毕，关闭所有链接
                os.close();
                is.close();

            } catch (IOException e) {
                continue;
            }
        }
    }