添加模版

{{if .Success}}
    <h1>Thanks for your message!</h1>
    <label>Email:</label><br />
    <label>{{.Details.Email}}</label><br />
    <label>Subject:</label><br />
    <label>{{.Details.Subject}}</label><br />
    <label>Message:</label><br />
    <label>{{.Details.Message}}</label>
{{else}}
    <h1>Contact</h1>
    <form method="POST">
        <label>Email:</label><br />
        <input type="text" name="email"><br />
        <label>Subject:</label><br />
        <input type="text" name="subject"><br />
        <label>Message:</label><br />
        <textarea name="message"></textarea><br />
        <input type="submit">
    </form>
{{end}}

读取模版

tmpl := template.Must(template.ParseFiles("forms.html"))

响应请求

func(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		tmpl.Execute(w, nil)
		return
	}

	details := ContactDetails{
		Email:   r.FormValue("email"),
		Subject: r.FormValue("subject"),
		Message: r.FormValue("message"),
	}
	tmpl.Execute(w, struct {
		Success bool
		Details ContactDetails
	}{true, details})
}

该响应方法中，先判断请求是否为post，如果不是，响应体写入模版并填入空数据；如果是，响应体写入模版并填入提交的数据。

完整代码

package main

import (
	"fmt"
	"html/template"
	"net/http"
)

type ContactDetails struct {
	Email   string
	Subject string
	Message string
}

func main() {
	tmpl := template.Must(template.ParseFiles("forms.html"))

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			tmpl.Execute(w, nil)
			return
		}

		details := ContactDetails{
			Email:   r.FormValue("email"),
			Subject: r.FormValue("subject"),
			Message: r.FormValue("message"),
		}

		fmt.Println(details)

		tmpl.Execute(w, struct {
			Success bool
			Details ContactDetails
		}{true, details})
	})

	http.ListenAndServe(":8090", nil)
}