How to make an already developed project have url friendly for SEO?

If you are using MVC, in some file you will be generating the route record. Something similar to:

        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
        );

What we are going to do is create a new generic route record over the Default route:

        string name = "GenericUrl";
        string url = "{generic}";
        object defaults = new { controller = "Common", action = "GenericUrl" };
        object namespaces = new[] { "SampleWebApp.Controllers" };

        var route = new GenericPathRoute(url, new MvcRouteHandler()) {
            Defaults = new RouteValueDictionary(defaults),
            DataTokens = new RouteValueDictionary()
        };

        if (namespaces != null) {
            route.DataTokens["Namespaces"] = namespaces;
        }

        routes.Add(name, route);

This rule will capture all the url's and analyze them in a later function. If they are "known" you can redirect the destination, and if they are not, the execution will continue.

To analyze the url's we need a new class that derives from Route and we have to overload the GetRouteData method:

public class GenericPathRoute : Route {
    public GenericPathRoute(string url, IRouteHandler routeHandler) : base(url, routeHandler) { }
    public GenericPathRoute(string url, RouteValueDictionary defaults, IRouteHandler routeHandler) : base(url, defaults, routeHandler) { }
    public GenericPathRoute(string url, RouteValueDictionary defaults, RouteValueDictionary constraints, IRouteHandler routeHandler) : base(url, defaults, constraints, routeHandler) { }
    public GenericPathRoute(string url, RouteValueDictionary defaults, RouteValueDictionary constraints, RouteValueDictionary dataTokens, IRouteHandler routeHandler) : base(url, defaults, constraints, dataTokens, routeHandler) { }

    public override RouteData GetRouteData(HttpContextBase httpContext) {
        RouteData data = base.GetRouteData(httpContext);

        if (data != null) {
            var slug = data.Values["generic"] as string;

            if (slug == "xxx") {
                data.Values["controller"] = "Home";
                data.Values["action"] = "ProductDetails";
                data.Values["productid"] = 1;
                return data;
            }
        }

        return data;
    }
}

Within the method the slug variable rescues the content of the "generic" url and you can tweak it as you see fit. Whether parsing, searching in database, etc ...

The "productid" index is an example. In this case, it corresponds to the name of the controller action parameter.

public class HomeController : Controller {
    public ActionResult ProductDetails(int productid) {
        ...
    }
}

If it's an apache server serving urls, you can use mod_rewrite and the .htaccess file to handle the urls as variables, so that in the browser you can put: / product / 89002 / night-lamp, and this one happens as / ProductDetail? productId = 89002, note that the third part of the friendly url (night-time lamp) is not taken into account to make the query, but it is displayed and can be indexed by the search bots.