golang模版的使用

前言

大部分的编程语言都是库实现模版，也是为了巩固mvc模式下服务端的统治地位，模版是如此的重要它甚至能够检验一个语言的成功和失败。然后，如今的现状是，单页应用大行其道，模版的使用已经变的越来越少。可能比较牢不可破的场景还是在生产邮件实体的时候。这篇文章中，我会使用一个例子去介绍如何用golang的template包生成基于定义在文件中的模版文件生成邮件实体。尽力去展现这个包中最常用的一些特性。

golang 代码：

package main
import (
    "fmt"
    "html/template"
    "os"
    "time"
)
type Account struct {
    FirstName string
    LastName  string
}
type Purchase struct {
    Date          time.Time
    Description   string
    AmountInCents int
}
type Statement struct {
    FromDate  time.Time
    ToDate    time.Time
    Account   Account
    Purchases []Purchase
}
func formatAsDate(t time.Time) string {
    year, month, day := t.Date()
    return fmt.Sprintf("%d/%d/%d", day, month, year)
}
func formatAsDollars(valueInCents int) (string, error) {
    dollars := valueInCents / 100
    cents := valueInCents % 100
    return fmt.Sprintf("$%d.%2d", dollars, cents), nil
}
func urgentNote(acc Account) string {
    return fmt.Sprintf("You have earned 100 vip points that can be used for purchases")
}
func hello() string {
    return fmt.Sprintf("hello word!")
}
func createMockStatement() Statement {
    return Statement{
        FromDate: time.Date(2017, 1, 1, 0, 0, 0, 0, time.UTC),
        ToDate:   time.Date(2017, 2, 1, 0, 0, 0, 0, time.UTC),
        Account: Account{
            FirstName: "alias",
            LastName:  "liyu4",
        },
        Purchases: []Purchase{
            Purchase{
                Date:          time.Date(2017, 1, 1, 0, 0, 0, 0, time.UTC),
                Description:   "dell ultrasharp 24 monitor",
                AmountInCents: 23026,
            },
            Purchase{
                Date:          time.Date(2017, 1, 1, 0, 0, 0, 0, time.UTC),
                Description:   "macbook air",
                AmountInCents: 88821,
            },
        },
    }
}
func main() {
    fmap := template.FuncMap{
        "formatAsDollars": formatAsDollars,
        "formatAsDate":    formatAsDate,
        "urgentNote":      urgentNote,
        "hello":           hello,
    }
    t, err := template.New("email.tmpl").Funcs(fmap).ParseFiles("email.tmpl")
    if err != nil {
        panic(err)
    }
    //Execute applies a parsed template to the specified data object,
    //writing the output to wr. If an error occurs executing the template or writing its output,
    //execution stops, but partial results may already have been written to the output writer.
    //A template may be executed safely in parallel.
    if err := t.Execute(os.Stdout, createMockStatement()); nil != err {
        panic(err)
    }
}

这段代码中最重要的部分是数据结构和main函数，其他的函数唯一的目的是展示从模版中调用不同的办法。

模版文件 email.tmpl:

{{with .Account -}}
Dear {{.FirstName}} {{.LastName}},  
{{- end}}
Below are your account statement details for period from {{.FromDate | formatAsDate}} to {{.ToDate | formatAsDate}}.
{{if .Purchases -}}
    Your purchases:
    {{- range .Purchases }}
        {{ .Date | formatAsDate}} {{ printf "%-20s" .Description }} {{.AmountInCents | formatAsDollars -}}
    {{- end}}
{{- else}}
You didn't make any purchases during the period.  
{{- end}}
{{$note := urgentNote .Account -}}
{{if $note -}}
Note: {{$note}}  
{{- end}}
Best Wishes,  
Customer Service

输出：

Dear alias liyu4,
    Below are your account statement details for period from 1/1/2017 to 1/2/2017.
    Your purchases:
            1/1/2017 dell ultrasharp 24 monitor $230.26
	        1/1/2017 macbook air          $888.21
    Note: You have earned 100 vip points that can be used for purchases
    Best Wishes,
    Customer Service

原文： http://goinbigdata.com/example-of-using-templates-in-golang/