取得根URL

public static string GetUrlRoot()
        {
            string strTemp=""; 
            if(System.Web.HttpContext.Current.Request.ServerVariables["HTTPS"] == "off") 
            { 
                strTemp = "http://"; 
            } 
            else 
            { 
                strTemp = "https://"; 
            } 

            strTemp = strTemp + System.Web.HttpContext.Current.Request.ServerVariables["SERVER_NAME"]; 

            if(System.Web.HttpContext.Current.Request.ServerVariables["SERVER_PORT"] != "80") 
            { 
                strTemp = strTemp + ":" + System.Web.HttpContext.Current.Request.ServerVariables["SERVER_PORT"]; 
            } 
            return strTemp;
        }