从网络上下载文件到本地

下载：

void downloadDemo() {
        String fileName = "E:" + File.separator + "test" + File.separator
                + "baidu.png";
        URL url = null;
        HttpsURLConnection connection = null;
        File file = new File(fileName);
        if (!file.exists()) {
            try {
                file.createNewFile();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        InputStream is = null;
        OutputStream os = null;
        byte[] b = new byte[1024];
        int len = 0;
        try {
            url = new URL("https://www.baidu.com/img/bdlogo.png");
            connection = (HttpsURLConnection) url.openConnection();
            is = connection.getInputStream();
            os = new FileOutputStream(file);
            while ((len = is.read(b)) != -1) {
                os.write(b, 0, len);
               //System.out.println(len);
            }
            System.out.println("download complete!" + file.length() + "   "
                    + connection.getContentLength());
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            try {
                is.close();
                os.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }
    }