C# 计算文件的MD5值

/// <summary>
/// 计算文件的MD5校验
/// </summary>
/// <param name="fileName"></param>
/// <returns></returns>
public static string GetMd5HashFromFile(string fileName)
{
    try
    {
        FileStream file = new FileStream(fileName, FileMode.Open);
        System.Security.Cryptography.MD5 md5 = new System.Security.Cryptography.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)
    {
        throw;
    }
}