Getting SharePoint Web Application URL Using SPAlternateUrl

By using SPAlternateURL object, you can get the URL or SharePoint 2010 Web Application since the alternate access mappings are associated with a Web Application. Sample code is provided below:

public static string GetWebAppURL(SPWebApplication oWebApp, SPUrlZone urlZone)
{
    string retVal = string.Empty;
    try
    {
        foreach (SPAlternateUrl altUrl in oWebApp.AlternateUrls)
        {
            if (altUrl.UrlZone == urlZone)
            {
                retVal = altUrl.Uri.ToString();
                break;
            }
        }
    }
    catch (Exception ex)
    {
        throw ex;
    }
    return retVal;
}

public static string GetWebAppURL(SPSite oSite, SPUrlZone urlZone)
{
    string retVal = string.Empty;
    SPWebApplication oWebApp = null;
    try
    {
        if ((oWebApp = oSite.WebApplication) != null)
            retVal = GetWebAppURL(oWebApp, urlZone);
    }
    catch (Exception ex)
    {
        throw ex;
    }
    return retVal;
}

public static string GetWebAppURL(SPWeb oWeb, SPUrlZone urlZone)
{
    string retVal = string.Empty;
    SPWebApplication oWebApp = null;
    try
    {
        if(( oWebApp = oWeb.Site.WebApplication)!=null)
            retVal = GetWebAppURL(oWebApp, urlZone);
    }
    catch (Exception ex)
    {
        throw ex;
    }
    return retVal;
}

In order to call these functions, you need to pass either SPWebApplication, SPSite or SPWeb object and specify the SPUrlZone enumeration which has the following originating zone of a request:

• Default - Specifies the default zone used for requests unless another zone is specified.
• Intranet - Specifies an intranet zone.
• Internet - Specifies an Internet zone.
• Custom - Specifies a custom zone.
• Extranet - Specifies an extranet zone.