c#：通过MD5得到文件和String的校验值

public static string GetMD5HashFromFile(string fileName)
{
try
{
FileStream file = new FileStream(fileName, System.IO.FileMode.Open, FileAccess.Read);
MD5 md5 = new MD5CryptoServiceProvider();
byte[] retVal = md5.ComputeHash(file);
file.Close();
StringBuilder sb = new StringBuilder();
for (int i = 0; i < retVal.Length; i++)
{
sb.Append(retVal[i].ToString("x2"));
}
return sb.ToString();
}
catch (Exception ex)
{
MyLog(LogPath , "Message " + System.DateTime.Now.ToLongTimeString() +" :"+ ex.Message);//MessageLog
return "no access";
//throw new Exception("GetMD5HashFromFile() fail,error:" + ex.Message);
}
}

public static string GetMD5HashFromFile(string strToHash)
{
try
{
MD5 md5 = new MD5CryptoServiceProvider();
byte[] bytes = System.Text.Encoding.UTF8.GetBytes(strToHash);
bytes = md5.ComputeHash(bytes);
md5.Clear();

String ret = "";
for (int i = 0; i < bytes.Length; i++)
{
ret += Convert.ToString(bytes[i], 16).PadLeft(2, '0');
}
return ret;
}
catch (Exception ex)
{
Console.WriteLine("Message " + System.DateTime.Now.ToLongTimeString() + " :" + ex.Message);//MessageLog
return "Md5 Error";
}
}