如何从网上下载视频并将其存储在本地设备上，然后使用视频播放器在Flutter应用程序上播放视频？

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:path_provider/path_provider.dart';
import 'dart:io';
import 'package:video_player/video_player.dart';

class VideoPlayerPage extends StatefulWidget {
  @override
  _VideoPlayerPageState createState() => _VideoPlayerPageState();
}

class _VideoPlayerPageState extends State<VideoPlayerPage> {
  VideoPlayerController _controller;
  Future<void> _initializeVideoPlayerFuture;

  @override
  void initState() {
    super.initState();
    _controller = VideoPlayerController.file(File('path_to_video_file'));
    _initializeVideoPlayerFuture = _controller.initialize();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  Future<void> _downloadAndSaveVideo() async {
    var videoUrl = 'url_to_video_file';
    var response = await http.get(videoUrl);
    var appDocDir = await getApplicationDocumentsDirectory();
    var videoFile = File('${appDocDir.path}/video.mp4');
    await videoFile.writeAsBytes(response.bodyBytes);
    setState(() {
      _controller = VideoPlayerController.file(videoFile);
      _initializeVideoPlayerFuture = _controller.initialize();
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Video Player'),
      ),
      body: FutureBuilder(
        future: _initializeVideoPlayerFuture,
        builder: (context, snapshot) {
          if (snapshot.connectionState == ConnectionState.done) {
            return AspectRatio(
              aspectRatio: _controller.value.aspectRatio,
              child: VideoPlayer(_controller),
            );
          } else {
            return Center(
              child: CircularProgressIndicator(),
            );
          }
        },
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _downloadAndSaveVideo,
        child: Icon(Icons.file_download),
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: VideoPlayerPage(),
  ));
}