add some MVC error handle examples

_examples/mvc/error-handler-hijack/main.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+	"github.com/kataras/iris/v12"
+	"github.com/kataras/iris/v12/mvc"
+)
+
+func main() {
+	app := iris.New()
+	app.RegisterView(iris.HTML("./views", ".html"))
+
+	// Hijack each output value of a method (can be used per-party too).
+	app.ConfigureContainer().
+		UseResultHandler(func(next iris.ResultHandler) iris.ResultHandler {
+			return func(ctx iris.Context, v interface{}) error {
+				switch val := v.(type) {
+				case errorResponse:
+					return next(ctx, errorView(val))
+				default:
+					return next(ctx, v)
+				}
+			}
+		})
+
+	m := mvc.New(app)
+	m.Handle(new(controller))
+
+	app.Listen(":8080")
+}
+
+func errorView(e errorResponse) mvc.Result {
+	switch e.Code {
+	case iris.StatusNotFound:
+		return mvc.View{Code: e.Code, Name: "404.html", Data: e}
+	default:
+		return mvc.View{Code: e.Code, Name: "500.html", Data: e}
+	}
+}
+
+type errorResponse struct {
+	Code    int
+	Message string
+}
+
+type controller struct{}
+
+type user struct {
+	ID uint64 `json:"id"`
+}
+
+func (c *controller) GetBy(userid uint64) interface{} {
+	if userid != 1 {
+		return errorResponse{
+			Code:    iris.StatusNotFound,
+			Message: "User Not Found",
+		}
+	}
+
+	return user{ID: userid}
+}