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

Former-commit-id: ed635ee95de7160cde11eaabc0c1dcb0e460a620

_examples/logging/file-logger/main.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"os"
+	"time"
+
+	"github.com/kataras/iris/v12"
+)
+
+func main() {
+	f := newLogFile()
+	defer f.Close()
+
+	app := iris.New()
+	// Attach the file as logger, remember, iris' app logger is just an io.Writer.
+	// Use the following code if you need to write the logs to file and console at the same time.
+	// app.Logger().SetOutput(io.MultiWriter(f, os.Stdout))
+	app.Logger().SetOutput(f)
+
+	app.Get("/ping", func(ctx iris.Context) {
+		// for the sake of simplicity, in order see the logs at the ./_today_.txt
+		ctx.Application().Logger().Infof("Request path: %s", ctx.Path())
+		ctx.WriteString("pong")
+	})
+
+	// Navigate to http://localhost:8080/ping
+	// and open the ./logs{TODAY}.txt file.
+	if err := app.Listen(":8080", iris.WithoutBanner); err != nil {
+		app.Logger().Warn("Shutdown with error: " + err.Error())
+	}
+}
+
+// Get a filename based on the date, just for the sugar.
+func todayFilename() string {
+	today := time.Now().Format("Jan 02 2006")
+	return today + ".txt"
+}
+
+func newLogFile() *os.File {
+	filename := todayFilename()
+	// Open the file, this will append to the today's file if server restarted.
+	f, err := os.OpenFile(filename, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
+	if err != nil {
+		panic(err)
+	}
+
+	return f
+}