C# -- 使用緩衝區進行文件下載操作

C# -- 使用緩衝區進行文件下載操作

1. 為避免下載超大文件占用記憶體資源，文件下載使用緩衝區，一點一點讀取文件資源。

    string str0 = @"ftp://localhost:21/xx/1.txt";
    string str1 = @"D:\2.txt";

    FtpWebRequest ftpWebRequest1 = (FtpWebRequest)WebRequest.Create(str0);
    ftpWebRequest1.KeepAlive = false;
    ftpWebRequest1.Method = WebRequestMethods.Ftp.GetFileSize;
    FtpWebResponse ftpWebResponse1 = (FtpWebResponse)ftpWebRequest1.GetResponse();
    long iContentLength1 = ftpWebResponse1.ContentLength;
    Console.WriteLine("FTP file content length:{0}位元組", iContentLength1);


    FtpWebRequest ftpWebRequest2 = (FtpWebRequest)WebRequest.Create(str0);
    ftpWebRequest2.Method = WebRequestMethods.Ftp.DownloadFile;
    FtpWebResponse ftpWebResponse2 = (FtpWebResponse)ftpWebRequest2.GetResponse();
    Stream stream = ftpWebResponse2.GetResponseStream();

    FileStream fileStream = new FileStream(str1, FileMode.Create);

    int BufferSize = 2* 1024 * 1024;
    byte[] Buffer = new byte[BufferSize];

    int iRead = 0;
    iRead = stream.Read(Buffer, 0, BufferSize);
    while (iRead > 0)
    {
        fileStream.Write(Buffer, 0, iRead);
        iRead = stream.Read(Buffer, 0, BufferSize);
    }

    stream.Close();
    fileStream.Close();

    FileInfo newFileInfo = new FileInfo(str1);
    long iContentLength2 = newFileInfo.Length;
    Console.WriteLine("Download file content lenth:{0}位元組", iContentLength2);
    Console.WriteLine("文件校驗：{0}", iContentLength1 == iContentLength2 ? "OK" : "文件大小不一樣");