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< 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.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" > < strong aria-hidden = "true" > 4.5.< / strong > JSON< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-06.html" > < strong aria-hidd
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2022-08-24 10:48:15 +00:00
< li > < em > KusonStack一站式可编程配置技术栈(Go): < a href = "https://github.com/KusionStack/kusion" > https://github.com/KusionStack/kusion< / a > < / em > < / li >
< li > < em > KCL 配置编程语言(Rust): < a href = "https://github.com/KusionStack/KCLVM" > https://github.com/KusionStack/KCLVM< / a > < / em > < / li >
< li > < em > 凹语言™: < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
2022-08-04 06:59:33 +00:00
< / ul >
< hr >
< h2 id = "77-httphandler接口" > < a class = "header" href = "#77-httphandler接口" > 7.7. http.Handler接口< / a > < / h2 >
< p > 在第一章中， （ ） （ ） ， ： < / p >
< p > < u > < i > net/http< / i > < / u > < / p >
< pre > < code class = "language-go" > package http
type Handler interface {
ServeHTTP(w ResponseWriter, r *Request)
}
func ListenAndServe(address string, h Handler) error
< / code > < / pre >
< p > ListenAndServe函数需要一个例如“localhost:8000”的服务器地址， ， （ ） ， < / p >
< p > 想象一个电子商务网站， ， ， ， < / p >
< p > < u > < i > gopl.io/ch7/http1< / i > < / u > < / p >
< pre > < code class = "language-go" > func main() {
db := database{" shoes" : 50, " socks" : 5}
log.Fatal(http.ListenAndServe(" localhost:8000" , db))
}
type dollars float32
func (d dollars) String() string { return fmt.Sprintf(" $%.2f" , d) }
type database map[string]dollars
func (db database) ServeHTTP(w http.ResponseWriter, req *http.Request) {
for item, price := range db {
fmt.Fprintf(w, " %s: %s\n" , item, price)
}
}
< / code > < / pre >
< p > 如果我们启动这个服务，< / p >
< pre > < code > $ go build gopl.io/ch7/http1
$ ./http1 &
< / code > < / pre >
< p > 然后用1.5节中的获取程序（ ） ， ： < / p >
< pre > < code > $ go build gopl.io/ch1/fetch
$ ./fetch http://localhost:8000
shoes: $50.00
socks: $5.00
< / code > < / pre >
< p > 目前为止， ， ， ， < / p >
< p > < u > < i > gopl.io/ch7/http2< / i > < / u > < / p >
< pre > < code class = "language-go" > func (db database) ServeHTTP(w http.ResponseWriter, req *http.Request) {
switch req.URL.Path {
case " /list" :
for item, price := range db {
fmt.Fprintf(w, " %s: %s\n" , item, price)
}
case " /price" :
item := req.URL.Query().Get(" item" )
price, ok := db[item]
if !ok {
w.WriteHeader(http.StatusNotFound) // 404
fmt.Fprintf(w, " no such item: %q\n" , item)
return
}
fmt.Fprintf(w, " %s\n" , price)
default:
w.WriteHeader(http.StatusNotFound) // 404
fmt.Fprintf(w, " no such page: %s\n" , req.URL)
}
}
< / code > < / pre >
< p > 现在handler基于URL的路径部分（ ） ， ； （ ， ） ， ： < / p >
< pre > < code class = "language-go" > msg := fmt.Sprintf(" no such page: %s\n" , req.URL)
http.Error(w, msg, http.StatusNotFound) // 404
< / code > < / pre >
< p > /price的case会调用URL的Query方法来将HTTP请求参数解析为一个map， < / p >
< p > 这里是一个和新服务器会话的例子：< / p >
< pre > < code > $ go build gopl.io/ch7/http2
$ go build gopl.io/ch1/fetch
$ ./http2 &
$ ./fetch http://localhost:8000/list
shoes: $50.00
socks: $5.00
$ ./fetch http://localhost:8000/price?item=socks
$5.00
$ ./fetch http://localhost:8000/price?item=shoes
$50.00
$ ./fetch http://localhost:8000/price?item=hat
no such item: " hat"
$ ./fetch http://localhost:8000/help
no such page: /help
< / code > < / pre >
< p > 显然我们可以继续向ServeHTTP方法中添加case， ， ， ； ， ， ：
而不需要考虑它后面的具体类型。< / p >
< p > 对于更复杂的应用， ， ， ， ， < / p >
< p > 在下面的程序中， ， < / p >
< p > < u > < i > gopl.io/ch7/http3< / i > < / u > < / p >
< pre > < code class = "language-go" > func main() {
db := database{" shoes" : 50, " socks" : 5}
mux := http.NewServeMux()
mux.Handle(" /list" , http.HandlerFunc(db.list))
mux.Handle(" /price" , http.HandlerFunc(db.price))
log.Fatal(http.ListenAndServe(" localhost:8000" , mux))
}
type database map[string]dollars
func (db database) list(w http.ResponseWriter, req *http.Request) {
for item, price := range db {
fmt.Fprintf(w, " %s: %s\n" , item, price)
}
}
func (db database) price(w http.ResponseWriter, req *http.Request) {
item := req.URL.Query().Get(" item" )
price, ok := db[item]
if !ok {
w.WriteHeader(http.StatusNotFound) // 404
fmt.Fprintf(w, " no such item: %q\n" , item)
return
}
fmt.Fprintf(w, " %s\n" , price)
}
< / code > < / pre >
< p > 让我们关注这两个注册到handlers上的调用。第一个db.list是一个方法值（ < / p >
< pre > < code class = "language-go" > func(w http.ResponseWriter, req *http.Request)
< / code > < / pre >
< p > 也就是说db.list的调用会援引一个接收者是db的database.list方法。所以db.list是一个实现了handler类似行为的函数， （ ： ） ， < / p >
< p > 语句http.HandlerFunc(db.list)是一个转换而非一个函数调用， ： < / p >
< p > < u > < i > net/http< / i > < / u > < / p >
< pre > < code class = "language-go" > package http
type HandlerFunc func(w ResponseWriter, r *Request)
func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
f(w, r)
}
< / code > < / pre >
< p > HandlerFunc显示了在Go语言接口机制中一些不同寻常的特点。这是一个实现了接口http.Handler的方法的函数类型。ServeHTTP方法的行为是调用了它的函数本身。因此HandlerFunc是一个让函数值满足一个接口的适配器， ， ： ， < / p >
< p > 因为handler通过这种方式注册非常普遍， ， ： < / p >
< p > < u > < i > gopl.io/ch7/http3a< / i > < / u > < / p >
< pre > < code class = "language-go" > mux.HandleFunc(" /list" , db.list)
mux.HandleFunc(" /price" , db.price)
< / code > < / pre >
< p > 从上面的代码很容易看出应该怎么构建一个程序： ， （ ） ， ， ， < / p >
< p > 所以为了方便， ， ， ； < / p >
< p > 然后服务器的主函数可以简化成：< / p >
< p > < u > < i > gopl.io/ch7/http4< / i > < / u > < / p >
< pre > < code class = "language-go" > func main() {
db := database{" shoes" : 50, " socks" : 5}
http.HandleFunc(" /list" , db.list)
http.HandleFunc(" /price" , db.price)
log.Fatal(http.ListenAndServe(" localhost:8000" , nil))
}
< / code > < / pre >
< p > 最后， ： ， ， ， ， < / p >
< p > < strong > 练习 7.11： < / strong > 增加额外的handler让客户端可以创建， ， ， < code > /update?item=socks& price=6< / code > 的请求会更新库存清单里一个货品的价格并且当这个货品不存在或价格无效时返回一个错误值。（注意：这个修改会引入变量同时更新的问题）< / p >
< p > < strong > 练习 7.12： < / strong > 修改/list的handler让它把输出打印成一个HTML的表格而不是文本。html/template包（ < / p >
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