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2023-06-26 17:30:52 +00:00
< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "../index.html" > Go语言圣经< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface-zh.html" > 译者序< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface.html" > 前言< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1.html" > < strong aria-hidden = "true" > 1.< / strong > 入门< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-01.html" > < strong aria-hidden = "true" > 1.1.< / strong > Hello, World< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-02.html" > < strong aria-hidden = "true" > 1.2.< / strong > 命令行参数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-03.html" > < strong aria-hidden = "true" > 1.3.< / strong > 查找重复的行< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-04.html" > < strong aria-hidden = "true" > 1.4.< / strong > GIF动画< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-05.html" > < strong aria-hidden = "true" > 1.5.< / strong > 获取URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-06.html" > < strong aria-hidden = "true" > 1.6.< / strong > 并发获取多个URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-07.html" > < strong aria-hidden = "true" > 1.7.< / strong > Web服务< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-08.html" > < strong aria-hidden = "true" > 1.8.< / strong > 本章要点< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2.html" > < strong aria-hidden = "true" > 2.< / strong > 程序结构< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-01.html" > < strong aria-hidden = "true" > 2.1.< / strong > 命名< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-02.html" > < strong aria-hidden = "true" > 2.2.< / strong > 声明< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-03.html" > < strong aria-hidden = "true" > 2.3.< / strong > 变量< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-04.html" > < strong aria-hidden = "true" > 2.4.< / strong > 赋值< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-05.html" > < strong aria-hidden = "true" > 2.5.< / strong > 类型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-06.html" > < strong aria-hidden = "true" > 2.6.< / strong > 包和文件< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-07.html" > < strong aria-hidden = "true" > 2.7.< / strong > 作用域< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3.html" > < strong aria-hidden = "true" > 3.< / strong > 基础数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-01.html" > < strong aria-hidden = "true" > 3.1.< / strong > 整型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-02.html" > < strong aria-hidden = "true" > 3.2.< / strong > 浮点数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-03.html" > < strong aria-hidden = "true" > 3.3.< / strong > 复数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-04.html" > < strong aria-hidden = "true" > 3.4.< / strong > 布尔型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-05.html" > < strong aria-hidden = "true" > 3.5.< / strong > 字符串< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-06.html" > < strong aria-hidden = "true" > 3.6.< / strong > 常量< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4.html" > < strong aria-hidden = "true" > 4.< / strong > 复合数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-01.html" > < strong aria-hidden = "true" > 4.1.< / strong > 数组< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-02.html" > < strong aria-hidden = "true" > 4.2.< / strong > Slice< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-03.html" > < strong aria-hidden = "true" > 4.3.< / strong > Map< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-04.html" > < strong aria-hidden = "true" > 4.4.< / strong > 结构体< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-05.html" class = "active" > < strong aria-hidden = "true" > 4.5.<
2022-08-04 06:59:33 +00:00
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2024-06-12 07:20:07 +00:00
< li > < em > Go语言圣经读书笔记(挖坑中...): < a href = "https://github.com/chai2010/gopl-notes-zh" > https://github.com/chai2010/gopl-notes-zh< / a > < / em > < / li >
< li > < em > 凹语言(Go实现, 面向WASM设计): < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
2023-06-26 17:46:27 +00:00
< / ul >
2022-08-04 06:59:33 +00:00
< hr >
< h2 id = "45-json" > < a class = "header" href = "#45-json" > 4.5. JSON< / a > < / h2 >
< p > JavaScript对象表示法（ ） ， （ ） ， ， ， < / p >
< p > Go语言对于这些标准格式的编码和解码都有良好的支持， （ ： ） ， ， < / p >
< p > JSON是对JavaScript中各种类型的值——字符串、数字、布尔值和对象——Unicode本文编码。它可以用有效可读的方式表示第三章的基础数据类型和本章的数组、slice、结构体和map等聚合数据类型。< / p >
< p > 基本的JSON类型有数字（ ） （ ） ， ， ， < code > \Uhhhh< / code > 转义数字来表示一个UTF-16编码（ ： ， ； ） ， < / p >
< p > 这些基础类型可以通过JSON的数组和对象类型进行递归组合。一个JSON数组是一个有序的值序列， ； ， ， ； （ ） ： < / p >
< pre > < code > boolean true
number -273.15
string " She said \" Hello, BF\" "
array [" gold" , " silver" , " bronze" ]
object {" year" : 1980,
" event" : " archery" ,
" medals" : [" gold" , " silver" , " bronze" ]}
< / code > < / pre >
< p > 考虑一个应用程序， （ ， ； ） < / p >
< p > < u > < i > gopl.io/ch4/movie< / i > < / u > < / p >
< pre > < code class = "language-Go" > type Movie struct {
Title string
Year int `json:" released" `
Color bool `json:" color,omitempty" `
Actors []string
}
var movies = []Movie{
{Title: " Casablanca" , Year: 1942, Color: false,
Actors: []string{" Humphrey Bogart" , " Ingrid Bergman" }},
{Title: " Cool Hand Luke" , Year: 1967, Color: true,
Actors: []string{" Paul Newman" }},
{Title: " Bullitt" , Year: 1968, Color: true,
Actors: []string{" Steve McQueen" , " Jacqueline Bisset" }},
// ...
}
< / code > < / pre >
< p > 这样的数据结构特别适合JSON格式， （ ） ： < / p >
< pre > < code class = "language-Go" > data, err := json.Marshal(movies)
if err != nil {
log.Fatalf(" JSON marshaling failed: %s" , err)
}
fmt.Printf(" %s\n" , data)
< / code > < / pre >
< p > Marshal函数返回一个编码后的字节slice， ， ； ： < / p >
< pre > < code > [{" Title" :" Casablanca" ," released" :1942," Actors" :[" Humphrey Bogart" ," Ingr
id Bergman" ]},{" Title" :" Cool Hand Luke" ," released" :1967," color" :true," Ac
tors" :[" Paul Newman" ]},{" Title" :" Bullitt" ," released" :1968," color" :true,"
Actors" :[" Steve McQueen" ," Jacqueline Bisset" ]}]
< / code > < / pre >
< p > 这种紧凑的表示形式虽然包含了全部的信息， ， ： < / p >
< pre > < code class = "language-Go" > data, err := json.MarshalIndent(movies, " " , " " )
if err != nil {
log.Fatalf(" JSON marshaling failed: %s" , err)
}
fmt.Printf(" %s\n" , data)
< / code > < / pre >
< p > 上面的代码将产生这样的输出（译注：在最后一个成员或元素后面并没有逗号分隔符）：< / p >
< pre > < code class = "language-Json" > [
{
" Title" : " Casablanca" ,
" released" : 1942,
" Actors" : [
" Humphrey Bogart" ,
" Ingrid Bergman"
]
},
{
" Title" : " Cool Hand Luke" ,
" released" : 1967,
" color" : true,
" Actors" : [
" Paul Newman"
]
},
{
" Title" : " Bullitt" ,
" released" : 1968,
" color" : true,
" Actors" : [
" Steve McQueen" ,
" Jacqueline Bisset"
]
}
]
< / code > < / pre >
< p > 在编码时， （ ， < / p >
< p > 细心的读者可能已经注意到， ， ： < / p >
< pre > < code > Year int `json:" released" `
Color bool `json:" color,omitempty" `
< / code > < / pre >
< p > 结构体的成员Tag可以是任意的字符串面值， " value" 键值对序列； ， ， ， ， （ ） ， ， < / p >
< p > 编码的逆操作是解码， ， ， ， ， ， ， < / p >
< pre > < code class = "language-Go" > var titles []struct{ Title string }
if err := json.Unmarshal(data, & titles); err != nil {
log.Fatalf(" JSON unmarshaling failed: %s" , err)
}
fmt.Println(titles) // " [{Casablanca} {Cool Hand Luke} {Bullitt}]"
< / code > < / pre >
< p > 许多web服务都提供JSON接口， ， ， ： < / p >
< p > < u > < i > gopl.io/ch4/github< / i > < / u > < / p >
< pre > < code class = "language-Go" > // Package github provides a Go API for the GitHub issue tracker.
// See https://developer.github.com/v3/search/#search-issues.
package github
import " time"
const IssuesURL = " https://api.github.com/search/issues"
type IssuesSearchResult struct {
TotalCount int `json:" total_count" `
Items []*Issue
}
type Issue struct {
Number int
HTMLURL string `json:" html_url" `
Title string
State string
User *User
CreatedAt time.Time `json:" created_at" `
Body string // in Markdown format
}
type User struct {
Login string
HTMLURL string `json:" html_url" `
}
< / code > < / pre >
< p > 和前面一样， ， ， ， ， < / p >
< p > SearchIssues函数发出一个HTTP请求， < code > ?< / code > 和< code > & < / code > 之类的特殊字符， ， < / p >
< p > < u > < i > gopl.io/ch4/github< / i > < / u > < / p >
< pre > < code class = "language-Go" > package github
import (
" encoding/json"
" fmt"
" net/http"
" net/url"
" strings"
)
// SearchIssues queries the GitHub issue tracker.
func SearchIssues(terms []string) (*IssuesSearchResult, error) {
q := url.QueryEscape(strings.Join(terms, " " ))
resp, err := http.Get(IssuesURL + " ?q=" + q)
if err != nil {
return nil, err
}
// We must close resp.Body on all execution paths.
// (Chapter 5 presents 'defer', which makes this simpler.)
if resp.StatusCode != http.StatusOK {
resp.Body.Close()
return nil, fmt.Errorf(" search query failed: %s" , resp.Status)
}
var result IssuesSearchResult
if err := json.NewDecoder(resp.Body).Decode(& result); err != nil {
resp.Body.Close()
return nil, err
}
resp.Body.Close()
return & result, nil
}
< / code > < / pre >
< p > 在早些的例子中， ， ， ， ， < / p >
< p > 我们调用Decode方法来填充变量。这里有多种方法可以格式化结构。下面是最简单的一种， ， < / p >
< p > < u > < i > gopl.io/ch4/issues< / i > < / u > < / p >
< pre > < code class = "language-Go" > // Issues prints a table of GitHub issues matching the search terms.
package main
import (
" fmt"
" log"
" os"
" gopl.io/ch4/github"
)
func main() {
result, err := github.SearchIssues(os.Args[1:])
if err != nil {
log.Fatal(err)
}
fmt.Printf(" %d issues:\n" , result.TotalCount)
for _, item := range result.Items {
fmt.Printf(" #%-5d %9.9s %.55s\n" ,
item.Number, item.User.Login, item.Title)
}
}
< / code > < / pre >
< p > 通过命令行参数指定检索条件。下面的命令是查询Go语言项目中和JSON解码相关的问题， ： < / p >
< pre > < code > $ go build gopl.io/ch4/issues
$ ./issues repo:golang/go is:open json decoder
13 issues:
#5680 eaigner encoding/json: set key converter on en/decoder
#6050 gopherbot encoding/json: provide tokenizer
#8658 gopherbot encoding/json: use bufio
#8462 kortschak encoding/json: UnmarshalText confuses json.Unmarshal
#5901 rsc encoding/json: allow override type marshaling
#9812 klauspost encoding/json: string tag not symmetric
#7872 extempora encoding/json: Encoder internally buffers full output
#9650 cespare encoding/json: Decoding gives errPhase when unmarshalin
#6716 gopherbot encoding/json: include field name in unmarshal error me
#6901 lukescott encoding/json, encoding/xml: option to treat unknown fi
#6384 joeshaw encoding/json: encode precise floating point integers u
#6647 btracey x/tools/cmd/godoc: display type kind of each named type
#4237 gjemiller encoding/base64: URLEncoding padding is optional
< / code > < / pre >
< p > GitHub的Web服务接口 https://developer.github.com/v3/ 包含了更多的特性。< / p >
< p > < strong > 练习 4.10： < / strong > 修改issues程序， ， < / p >
< p > < strong > 练习 4.11： < / strong > 编写一个工具， ， < / p >
< p > < strong > 练习 4.12： < / strong > 流行的web漫画服务xkcd也提供了JSON接口。例如， （ ） ， ， < / p >
< p > < strong > 练习 4.13： < / strong > 使用开放电影数据库的JSON服务接口， ， ， < / p >
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