add experimental handlers examples

Former-commit-id: 8d8a0d15afce2554dc5926f6b9bd9c42cb95dad0

_examples/experimental-handlers/prometheus/simple/main.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"math/rand"
+	"time"
+
+	"github.com/kataras/iris"
+
+	prometheusMiddleware "github.com/iris-contrib/middleware/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+func main() {
+	app := iris.New()
+	m := prometheusMiddleware.New("serviceName", 0.3, 1.2, 5.0)
+
+	app.Use(m.ServeHTTP)
+
+	app.OnErrorCode(iris.StatusNotFound, func(ctx iris.Context) {
+		// error code handlers are not sharing the same middleware as other routes, so we have
+		// to call them inside their body.
+		m.ServeHTTP(ctx)
+
+		ctx.Writef("Not Found")
+	})
+
+	app.Get("/", func(ctx iris.Context) {
+		sleep := rand.Intn(4999) + 1
+		time.Sleep(time.Duration(sleep) * time.Millisecond)
+		ctx.Writef("Slept for %d milliseconds", sleep)
+	})
+
+	app.Get("/metrics", iris.FromStd(promhttp.Handler()))
+
+	// http://localhost:8080/
+	// http://localhost:8080/anotfound
+	// http://localhost:8080/metrics
+	app.Run(iris.Addr(":8080"))
+}