asp.net 获取系统的根目录

测试有效的：系统的根目录

HttpContext.Current.Server.MapPath(HttpContext.Current.Request.ApplicationPath).ToLower();

以下为参考：

ASP.NET根路径的获取和将Web站点下的绝对路径转换为虚拟路径的两种方案

ASP.NET 根路径的获取
        private string _ApplicationPath;
        /// <summary>
        /// 虚拟应用程序根路径
        /// </summary>
        public string ApplicationPath
        {
            get
            {
                _ApplicationPath = HttpContext.Current.Request.ApplicationPath;
                if (_ApplicationPath.Length == 1)
                {
                    _ApplicationPath = "";
                }
                return _ApplicationPath;
            }
        }
        private string _CurrentPath;
        /// <summary>
        /// 当前的绝对路径
        /// </summary>
        public string CurrentPath
        {
            get
            {
                _CurrentPath = HttpContext.Current.Server.MapPath(".").ToLower();//当前的绝对路径(这里MapPath里的"."代表当前服务器)

                if (_CurrentPath.Length == 1)
                {
                    _CurrentPath = "";
                }
                return _CurrentPath;
            }
        }
        private string _RootPath;
        /// <summary>
        /// 系统的根目录
        /// </summary>
        public string RootPath
        {
            get
            {

                _RootPath = HttpContext.Current.Server.MapPath(HttpContext.Current.Request.ApplicationPath).ToLower();//当前的绝对路径
                if (_RootPath.Length == 1)
                {
                    _RootPath = "";
                }
                return _RootPath;
            }
        }

将Web站点下的绝对路径转换为相对于指定页面的虚拟路径

第一个方法
/**//// <summary>
///

将Web站点下的绝对路径转换为相对于指定页面的虚拟路径
/// </summary>
/// <param name="page">当前页面指针，一般为this</param>
/// <param name="specifiedPath">绝对路径</param>
/// <returns>虚拟路径, 型如: http://www.cnblogs.com/</returns>
public static string ConvertSpecifiedPathToRelativePathForPage(Page page, string specifiedPath)
{
    // 根目录虚拟路径
    string virtualPath = page.Request.ApplicationPath;
    // 根目录绝对路径
    string pathRooted = HostingEnvironment.MapPath(virtualPath);
    // 页面虚拟路径
    string pageVirtualPath = page.Request.Path;

    if (!Path.IsPathRooted(specifiedPath) || specifiedPath.IndexOf(pathRooted) == -1)
    {
        throw new Exception(string.Format(""{0}"是虚拟路径而不是绝对路径!", specifiedPath));
    }

    // 转换成相对路径
    //(测试发现，pathRooted 在 VS2005 自带的服务器跟在IIS下根目录或者虚拟目录运行似乎不一样,
    // 有此地方后面会加"", 有些则不会, 为保险起见判断一下)
    if (pathRooted.Substring(pathRooted.Length - 1, 1) == "\")
    {
        specifiedPath = specifiedPath.Replace(pathRooted, "/");
    }
    else
    {
        specifiedPath = specifiedPath.Replace(pathRooted, "");
    }

string relativePath = specifiedPath.Replace("\", "/");

string[] pageNodes = pageVirtualPath.Split('/');

// 减去最后一个页面和前面一个 "" 值
int pageNodesCount = pageNodes.Length - 2;

    for (int i = 0; i < pageNodesCount; i  )
    {
        relativePath = "/.."   relativePath;
    }

    if (pageNodesCount > 0)
    {
        // 如果存在 ".." , 则把最前面的 "/" 去掉
        relativePath = relativePath.Substring(1, relativePath.Length - 1);
    }

return relativePath;
}

第二个方法

将Web站点下的绝对路径转换为虚拟路径
/**//// <summary>
/// 将Web站点下的绝对路径转换为虚拟路径
/// 注：非Web站点下的则不转换
/// </summary>
/// <param name="page">当前页面指针，一般为this</param>
/// <param name="specifiedPath">绝对路径</param>
/// <returns>虚拟路径, 型如: ~/</returns>
public static string ConvertSpecifiedPathToRelativePath(Page page, string specifiedPath)
{
string virtualPath = page.Request.ApplicationPath;

string pathRooted = HostingEnvironment.MapPath(virtualPath);

    if (!Path.IsPathRooted(specifiedPath) || specifiedPath.IndexOf(pathRooted) == -1)
    {
        return specifiedPath;
    }

    if (pathRooted.Substring(pathRooted.Length - 1, 1) == "\")
    {
        specifiedPath = specifiedPath.Replace(pathRooted, "~/");
    }
    else
    {
        specifiedPath = specifiedPath.Replace(pathRooted, "~");
    }

string relativePath = specifiedPath.Replace("\", "/");
return relativePath;
}

将虚拟路径转绝对路就没什么好说的了