/// <summary>
/// Http下載文件
/// </summary>
public static string HttpDownloadFile(string url, string path)
{
    // 設置參數
    HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;

    //發送請求并獲取相應回應數據
    HttpWebResponse response = request.GetResponse() as HttpWebResponse;
    //直到request.GetResponse()程序才開始向目標網頁發送Post請求
    Stream responseStream = response.GetResponseStream();

    //創建本地文件寫入流
    Stream stream = new FileStream(path, FileMode.Create);

    byte[] bArr = new byte[1024];
    int size = responseStream.Read(bArr, 0, (int)bArr.Length);
    while (size > 0)
    {
        stream.Write(bArr, 0, size);
        size = responseStream.Read(bArr, 0, (int)bArr.Length);
    }
    stream.Close();
    responseStream.Close();
    return path;
}