获得文件的Hash编码

 /// <summary>
  /// 获得文件的hash代码
  /// </summary>
  /// <param name="strFileName">文件全名</param>
  /// <returns></returns>
  public static string GetFileHash(string strFileName)
  {
   if(strFileName==null || strFileName.Equals(""))
   {
    return string.Empty;
   }

   if(!File.Exists(strFileName))
   {
    return string.Empty;
   }

   HashAlgorithm hasher= new MD5CryptoServiceProvider();
   StringBuilder buffer=new StringBuilder();
   try
   {
    using(FileStream f=new FileStream(strFileName,FileMode.Open,FileAccess.Read,FileShare.Read,8192))
    {
     hasher.ComputeHash(f);
     byte [] hash = hasher.Hash;
     foreach(byte bt in hash)
     {
      buffer.Append(string.Format("{0:x2}",bt));
     }
    }
   }
   catch(Exception ex)
   {
    System.Diagnostics.Debug.WriteLine(ex.Message);
    return "";
   }
   return buffer.ToString();
  }