1    public class WebDown
  2     {
  4         /// 下載檔案方法
  6         /// 檔案儲存路徑和檔名
  7         /// 返回伺服器檔名
  9         public static bool DeownloadFile(string sourceFile, string desFile)
 10         {
 11             bool flag = false;
 12             long SPosition = 0;
 13             FileStream FStream = null
 
;
 14             Stream myStream = null;
 15             string fileName = sourceFile.Substring(sourceFile.LastIndexOf(@"/") + 1);
 16             if (desFile.EndsWith("\\"))
 17             {
 18                 desFile = desFile + fileName;
 19             }
 20             else
 21             {
 22
 
                 desFile = desFile + "\\" + fileName;
 23             }
 24             try
 25             {
 26                 //判斷要下載的資料夾是否存在
 27                 if (File.Exists(desFile))
 28                 {
 29                     //開啟上次下載的檔案
 30                     FStream = File.OpenWrite(desFile);
 
 31                     //獲取已經下載的長度
 32                     SPosition = FStream.Length;
 33                     long serverFileLength = GetHttpLength(sourceFile);
 34                     if (SPosition == serverFileLength)
 35                     {//檔案是完整的，直接結束下載任務
 36                         return true;
 37                     }
 38                     FStream.Seek(SPosition, SeekOrigin.Current);
 39                 }
 40                 else
 41                 {
 42                     //檔案不儲存建立一個檔案
 43                     FStream = new FileStream(desFile, FileMode.Create);
 44                     SPosition = 0;
 45                 }
 46                 //開啟網路連線
 47                 HttpWebRequest myRequest = (HttpWebRequest)HttpWebRequest.Create(sourceFile);
 48                 if (SPosition > 0)
 49                 {
 50                     myRequest.AddRange(SPosition);             //設定Range值
 51                 }
 52                 //向伺服器請求,獲得伺服器的迴應資料流
 53                 myStream = myRequest.GetResponse().GetResponseStream();
 54                 //定義一個位元組資料
 55                 byte[] btContent = new byte[512];
 56                 int intSize = 0;
 57                 intSize = myStream.Read(btContent, 0, 512);
 58                 while (intSize > 0)
 59                 {
 60                     FStream.Write(btContent, 0, intSize);
 61                     intSize = myStream.Read(btContent, 0, 512);
 62                 }
 63                 flag = true;        //返回true下載成功
 64             }
 65             catch (Exception ex)
 66             {
 67                 SysLog.WriteTxtLog("下載檔案時異常：" + ex.Message);
 68             }
 69             finally
 70             {
 71                 //關閉流
 72                 if (myStream != null)
 73                 {
 74                     myStream.Close();
 75                     myStream.Dispose();
 76                 }
 77                 if (FStream != null)
 78                 {
 79                     FStream.Close();
 80                     FStream.Dispose();
 81                 }
 82             }
 83             return flag;
 84         }
 85         static long GetHttpLength(string url)
 86         {
 87             long length = 0;
 88             try
 89             {
 90                 var req = (HttpWebRequest)WebRequest.CreateDefault(new Uri(url));
 91                 req.Method = "HEAD";
 92                 req.Timeout = 5000;
 93                 var res = (HttpWebResponse)req.GetResponse();
 94                 if (res.StatusCode == HttpStatusCode.OK)
 95                 {
 96                     length = res.ContentLength;
 97                 }
 98                 res.Close();
 99                 return length;
100             }
101             catch (WebException wex)
102             {
103                 return 0;
104             }
105         }
106     }