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

Former-commit-id: ed635ee95de7160cde11eaabc0c1dcb0e460a620

_examples/logging/request-logger/main.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"github.com/kataras/iris/v12"
+	"github.com/kataras/iris/v12/middleware/logger"
+)
+
+func main() {
+	app := iris.New()
+
+	customLogger := logger.New(logger.Config{
+		// Status displays status code
+		Status: true,
+		// IP displays request's remote address
+		IP: true,
+		// Method displays the http method
+		Method: true,
+		// Path displays the request path
+		Path: true,
+		// Query appends the url query to the Path.
+		Query: true,
+
+		// Columns: true,
+
+		// if !empty then its contents derives from `ctx.Values().Get("logger_message")
+		// will be added to the logs.
+		MessageContextKeys: []string{"logger_message"},
+
+		// if !empty then its contents derives from `ctx.GetHeader("User-Agent")
+		MessageHeaderKeys: []string{"User-Agent"},
+	})
+
+	app.Use(customLogger)
+
+	h := func(ctx iris.Context) {
+		ctx.Writef("Hello from %s", ctx.Path())
+	}
+	app.Get("/", h)
+
+	app.Get("/1", h)
+
+	app.Get("/2", h)
+
+	// http errors have their own handlers, therefore
+	// registering a middleare should be done manually.
+	/*
+	 app.OnErrorCode(404 ,customLogger, func(ctx iris.Context) {
+	 	ctx.Writef("My Custom 404 error page ")
+	 })
+	*/
+	// or catch all http errors:
+	app.OnAnyErrorCode(customLogger, func(ctx iris.Context) {
+		// this should be added to the logs, at the end because of the `logger.Config#MessageContextKey`
+		ctx.Values().Set("logger_message",
+			"a dynamic message passed to the logs")
+		ctx.Writef("My Custom error page")
+	})
+
+	// http://localhost:8080
+	// http://localhost:8080/1
+	// http://localhost:8080/2
+	// http://lcoalhost:8080/notfoundhere
+	// see the output on the console.
+	app.Listen(":8080")
+}