How to get full host name + port number in Application_Start of Global.aspx?

I tried

Uri uri = HttpContext.Current.Request.Url;
String host = uri.Scheme + Uri.SchemeDelimiter + uri.Host + ":" + uri.Port;

and it worked well on my local machine, but when being published to IIS7, there is an exception saying

System.Web.HttpException: Request 开发者_StackOverflow社区is not available in this context

Anyone know how to achieve this?

When your web application starts, there is no HTTP request being handled.

You may want to handle define the Application_BeginRequest(Object Sender, EventArgs e) method in which the the Request context is available.

Edit: Here is a code sample inspired by the Mike Volodarsky's blog that Michael Shimmins linked to:

    void Application_BeginRequest(Object source, EventArgs e)
    {
        HttpApplication app = (HttpApplication)source;
        var host = FirstRequestInitialisation.Initialise(app.Context);
    }

    static class FirstRequestInitialisation
    {
        private static string host = null;
        private static Object s_lock = new Object();

        // Initialise only on the first request
        public static string Initialise(HttpContext context)
        {
            if (string.IsNullOrEmpty(host))
            {
                lock (s_lock)
                {
                    if (string.IsNullOrEmpty(host))
                    {
                        var uri = context.Request.Url;
                        host = uri.GetLeftPart(UriPartial.Authority);
                    }
                }
            }

            return host;
        }
    }

The accepted answer is good, but in most cases (if the first request is a HTTP Request) you should better use the Session_Start event, which is called once per user every 20 minutes or so (not sure how long the session is valid). Application_BeginRequest will be fired at every Request.

public void Session_Start(Object source, EventArgs e)
{
   //Request / Request.Url is available here :)
}

Just answering this so if someone ever decides to actually search on this topic...

This works on application start in any mode...

typeof(HttpContext).GetField("_request", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(HttpContext.Current)