implemented decorator pattern

concurrency/barrier/barrier.go

@@ -0,0 +1,2 @@
+package barrier
+

structural/decorator/decorator.go

@@ -0,0 +1,31 @@
+package decorator
+
+import (
+	"os"
+	"io"
+	"fmt"
+	"net/http"
+)
+
+// simple http server
+type SimpleServer struct{
+	msg string
+}
+func (s *SimpleServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprintln(w, s.msg)
+}
+
+// log decorator for simple server
+type ServerWithLog struct {
+	handler http.Handler
+	logger  io.Writer
+}
+func (s *ServerWithLog) ServeHTTP(w http.ResponseWriter, r *http.Request)  {
+	fmt.Fprintf(s.logger, "Got request with uri: %s \n", r.RequestURI)
+	s.handler.ServeHTTP(w, r)
+}
+
+func Demo(){
+	http.Handle("/", &ServerWithLog{&SimpleServer{"Simple server"}, os.Stdout})
+	http.ListenAndServe(":3000", nil)
+}