public static bool DownLoadFile(string serverFile, string localFile)
        {
            try
            {
                WebRequest request = WebRequest.Create(serverFile);
                WebResponse response = request.GetResponse();
                long fileLength = response.ContentLength;
                byte[] buffer = new byte[fileLength];
                long bufferLength = fileLength;
                int maxReadCount = bufferLength > int.MaxValue ? int.MaxValue : buffer.Length;
                int startPos = 0;
                using (Stream stream = response.GetResponseStream())
                {
                    while (bufferLength > 0)
                    {
                        int downByte = stream.Read(buffer, startPos, maxReadCount);
                        if (downByte <= 0) { break; }
                        startPos += downByte;
                        bufferLength -= downByte;
                        maxReadCount -= downByte;
                    }
                    using (FileStream fs = new FileStream(localFile, FileMode.Create, FileAccess.Write))
                    {
                        fs.Write(buffer, 0, buffer.Length);
                        stream.Close();
                        fs.Close();
                    }
                }

                return true;
            }
            catch (Exception ex)
            {
                Utility.GetInstance().Logger.Error("下载文件出错:"+ex.Message);
                return false;
            }
        }