我的端口一直监听不到怎么回事

package main

import (
   "fmt"
   "net/http"
)

func main()  {
   http.HandleFunc("/", func(writer http.ResponseWriter, request *http.Request) {
      fmt.Fprintln(writer,"hello world");
   })

   http.ListenAndServe("127.0.0.1:9090",nil);
}