/// <summary>
/// Http下载文件
/// </summary>
public static string HttpDownloadFile(string url, string path)
{
    // 设置参数
    HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;

    //发送请求并获取相应回应数据
    HttpWebResponse response = request.GetResponse() as HttpWebResponse;
    //直到request.GetResponse()程序才开始向目标网页发送Post请求
    Stream responseStream = response.GetResponseStream();

    //创建本地文件写入流
    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;
}