C# get请求远程文件，把它保存到本地

代码如下：后续进行解释

   public string CopyFileByUrl(string url)
        {
            string name = System.Web.HttpUtility.UrlDecode(url.Substring(url.LastIndexOf('/') + 1));//获取名字
            string fileFolder = @"F:\AAA\";
            string filePath = Path.Combine(fileFolder, name);//存放地址就是本地的upload下的同名的文件
            if (!Directory.Exists(fileFolder))
                Directory.CreateDirectory(fileFolder);

            string returnPath = GetSimplePath(filePath);//需要返回的路径
            if (File.Exists(filePath))
            {//如果已经存在，那么就不需要拷贝了，如果没有，那么就进行拷贝
                return returnPath;
            }
            HttpWebRequest request = HttpWebRequest.Create(url) as HttpWebRequest;
            request.Method = "GET";
            request.ProtocolVersion = new Version(1, 1);
            HttpWebResponse response = request.GetResponse() as HttpWebResponse;
            if (response.StatusCode == HttpStatusCode.NotFound)
            {
                return string.Empty;//找不到则直接返回null
            }
            // 转换为byte类型
            System.IO.Stream stream = response.GetResponseStream();


            //创建本地文件写入流
            Stream fs = new FileStream(filePath, FileMode.Create);
            byte[] bArr = new byte[1024];
            int size = stream.Read(bArr, 0, (int)bArr.Length);
            while (size > 0)
            {
                fs.Write(bArr, 0, size);
                size = stream.Read(bArr, 0, (int)bArr.Length);
            }
            fs.Close();
            stream.Close();
            return returnPath;
        }