reorganization of _examples and add some new examples such as iris+groupcache+mysql+docker

Former-commit-id: ed635ee95de7160cde11eaabc0c1dcb0e460a620

_examples/http-server/notify-on-shutdown/main.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+	"context"
+	"time"
+
+	"github.com/kataras/iris/v12"
+)
+
+func main() {
+	app := iris.New()
+
+	app.Get("/", func(ctx iris.Context) {
+		ctx.HTML("<h1>Hello, try to refresh the page after ~5 secs</h1>")
+	})
+
+	app.Logger().Info("Wait 5 seconds and check your terminal again")
+	// simulate a shutdown action here...
+	go func() {
+		<-time.After(5 * time.Second)
+		timeout := 10 * time.Second
+		ctx, cancel := context.WithTimeout(context.Background(), timeout)
+		defer cancel()
+		// close all hosts, this will notify the callback we had register
+		// inside the `configureHost` func.
+		app.Shutdown(ctx)
+	}()
+
+	// app.ConfigureHost(configureHost) -> or pass "configureHost" as `app.Addr` argument, same result.
+
+	// start the server as usual, the only difference is that
+	// we're adding a second (optional) function
+	// to configure the just-created host supervisor.
+	//
+	// http://localhost:8080
+	// wait 10 seconds and check your terminal.
+	app.Run(iris.Addr(":8080", configureHost), iris.WithoutServerError(iris.ErrServerClosed))
+
+	time.Sleep(500 * time.Millisecond) // give time to the separate go routine(`onServerShutdown`) to finish.
+
+	/* See
+	iris.RegisterOnInterrupt(callback) for global catch of the CTRL/CMD+C and OS events.
+	Look at the "graceful-shutdown" example for more.
+	*/
+}
+
+func onServerShutdown() {
+	println("server is closed")
+}
+
+func configureHost(su *iris.Supervisor) {
+	// here we have full access to the host that will be created
+	// inside the `app.Run` function or `NewHost`.
+	//
+	// we're registering a shutdown "event" callback here:
+	su.RegisterOnShutdown(onServerShutdown)
+	// su.RegisterOnError
+	// su.RegisterOnServe
+}