我正在跟蹤 go tour，其中一個練習要求我構建幾個 http 處理程序。這是代碼：    package mainimport (    "fmt"    "net/http")type String stringtype Struct struct {  Greeting string  Punct string  Who string}func (s String) ServeHTTP(w http.ResponseWriter, r *http.Request){    fmt.Fprint(w, s)}func (s *Struct) ServeHTTP(w http.ResponseWriter, r *http.Request){  fmt.Fprint(w, "This is a struct. Yey!")}func main() {    // your http.Handle calls here    http.ListenAndServe("localhost:4000", nil)    http.Handle("/string", String("I'm a frayed knot"))    http.Handle("/struct", &Struct{"Hello",":","Gophers!"})}代碼編譯并運行得很好但是我不確定為什么當我導航到localhost:4000/string或localhost:4000/struct我得到的只是來自默認 http 處理程序的 404 錯誤。我在這里遺漏了一步還是？