在asp.net 4.0中,我们可以像这样用http模块来重写模块

protected void Application_BeginRequest(Object sender, EventArgs e)
{
    string CountryCodeInUrl = "", redirectUrl="";
    var countryCode = CookieSettings.ReadCookie();
    if (countryCode=="")
    {
        countryCode = "gb";
    }

    if (HttpContext.Current.Request.RawUrl.Length >= 2)
    {
        CountryCodeInUrl = HttpContext.Current.Request.RawUrl.Substring(1, 2);
    }

    if (countryCode != CountryCodeInUrl)
    {
        if (HttpContext.Current.Request.RawUrl.Length >= 2)
        {
            if (HttpContext.Current.Request.RawUrl.Substring(1, 2) != "")
            {
                countryCode = HttpContext.Current.Request.RawUrl.Substring(1, 2);
            }
        }
        if(!System.Web.HttpContext.Current.Request.RawUrl.Contains(countryCode))
        {
            redirectUrl = string.Format("/{0}{1}", countryCode, System.Web.HttpContext.Current.Request.RawUrl);
        }
        else
        {
            redirectUrl = System.Web.HttpContext.Current.Request.RawUrl;
        }
        CookieSettings.SaveCookie(countryCode);
        System.Web.HttpContext.Current.Response.RedirectPermanent(redirectUrl);
    }   
}

现在告诉我如何在ASP.NET Core中通过中间件重写以上代码？

我刚刚读了这篇文章https://docs.microsoft.com/en-us/aspnet/core/migration/http-modules

请详细指导我.谢谢

解决方法:

您几乎只需要将代码移至中间件类,并使用Core HttpContext而不是System.Web.

这样的类如下所示：

//RedirectMiddleware.cs

public class RedirectMiddleware
{
    private readonly RequestDelegate _next;

    public RedirectMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        string CountryCodeInUrl = "", redirectUrl = "";
        var countryCode = CookieSettings.ReadCookie();
        if (countryCode == "")
        {
            countryCode = "gb";
        }

        if (context.Request.Path.Value.Length >= 2)
        {
            CountryCodeInUrl = context.Request.Path.Value.Substring(1, 2);
        }

        if (countryCode != CountryCodeInUrl)
        {
            if (context.Request.Path.Value.Length >= 2)
            {
                if (context.Request.Path.Value.Substring(1, 2) != "")
                {
                    countryCode = context.Request.Path.Value.Substring(1, 2);
                }
            }
            if (!context.Request.Path.Value.Contains(countryCode))
            {
                redirectUrl = string.Format("/{0}{1}", countryCode, context.Request.Path.Value);
            }
            else
            {
                redirectUrl = context.Request.Path.Value;
            }
            CookieSettings.SaveCookie(countryCode);
            context.Response.Redirect(redirectUrl, true);
        }

        await _next.Invoke(context);
    }
}

要使用它,您需要先注册Startup.cs文件,然后再注册MVC中间件,如下所示：

app.UseMiddleware<RedirectMiddleware>();

app.UseMvc(routes =>
{
    routes.MapRoute(
        name: "default",
        template: "{controller=Home}/{action=Index}/{id?}");
});

希望这会帮助您入门,有关中间件的更多信息,请参见this博客文章.