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MVC 3 - Handling 404 errors

Intr-un post anterior am promis ca o sa revin cu cativa pasi ce trebuie facuti pentru a putea face handling corect la o aplicatie ASP.NET MVC 3.
Mai jos o sa gasiti cei 3 pasi care trebuie facuti pentru a face handling la erorile de tip 404 cat mai bine, fara sa avem surprize neplacute cand aplicatia este deja in productie. Exista mai multe variante. Varianta aleasa de mine nu necesita existenta sau modificarea unui base controller.
1. Pentru toate erorile care apar in sistem avem nevoie de un loc comun
Toate erorile trebuie sa fie controlate dintr-un loc comun. In cazul in care vrem sa vedem la ce erori se face handling sau care este modalitatea prin care se face handling, ca sa nu cautam prin controale, cel mai usor este sa ne facem un controller care se ocupa doar cu acest lucru. public
class ErrorController
{
    public ActionResult Http404(string url)
    {
        Response.StatusCode = (int)HttpStatusCode.NotFound;
        var model = new ErrorViewModel();
        model.RequestedUrl = Request.Url.OriginalString.Contains(url) & Request.Url.OriginalString != url
                ? Request.Url.OriginalString
                : url;
        model.ReferrerUrl = Request.UrlReferrer != null
                && Request.UrlReferrer.OriginalString != model.RequestedUrl
                ? Request.UrlReferrer.OriginalString
                : null;
        return View("NotFound", model);
    }
}
In interiorul actiunii Http404 se pot scrie informatii in trace cu privire la eroarea aparuta.
2. Handling la erorile de tip 404 din fisierul de configurare
In web.config trebuie sa facem handling la erorile de tip 404 in doua locatii.
<system.webServer>
    <httpErrors errorMode="Custom">
      <remove statusCode="404" subStatusCode="-1" />
      <error statusCode="404" path="/Error/Http404" responseMode="ExecuteURL" />
      <remove statusCode="500" subStatusCode="-1" />
      <error statusCode="500" path="/Error/ServerError" responseMode="ExecuteURL" />
    </httpErrors>   
<system.webServer>
</system.web>
si
<system.web>
    <customErrors mode="On" defaultRedirect="/Error/Http404">
      <error statusCode="404" redirect="/Error/ServerError" />
    </customErrors>
</system.web>
De foarte multe ori se uita de sectiune httpErrors, care poate sa genereze uneori probleme.
3. Global.asax - custom routes
Cand definim "tabela" pentru routes, nu trebuie sa uitam sa mapam erorile de tip 404 si sa le redirectionam spre controlerul de erori.
routes.MapRoute(
        "Error - 404",
        "NotFound",
        new { controller = "Error", action = "Http404" }
        );
    routes.MapRoute(
        "Error - 500",
        "ServerError",
        new { controller = "Error", action = "ServerError"}
        );
Este foarte important ca aceste doua route sa fie primele definite. Dupa aceste route putem sa adaugam cele custom pentru aplicatia noastra.

Exista si alte variante. Aceasta mi s-a parut destul ca nu genereaza modificari de cod si in alte zone, unde poate nu vrem sa facem nici o modificare.

Comments

  1. Interesant - mai greu e de decis ce sa apara in pagina de 404 not found - macar un link care sa duca user-ul inapoi la aplicatie, poate un feature de search cand e posibil: http://www.codinghorror.com/blog/2007/03/creating-user-friendly-404-pages.html

    ReplyDelete
  2. Dar daca toata aplicatia este down se poate crea o bucla din cauza redirectariilor. Trebuie avut grija daca folosim un controller pentru Erori, ca acesta sa fie cat mai simplu si de evitat sa mosteneasca din ceva BaseController a aplicatiei noastre.
    Cea mai sigura varianta pagini HTML simple.

    ReplyDelete
  3. Mie personal mi se pare gresit (dpdv SEO) sa redirectionezi in caz de URL inexistent. In mod normal ar trebui sa raspunzi cu 404 si URL-ul sa nu se schimbe in browser.

    ReplyDelete
    Replies
    1. Exista cazuri cand eroarea 404 iti scapa din cod si aici e ultimul loc unde o poti prinde (sau din cod, dar tot pe baza unei configurati asemanatoare).

      Delete

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