golang是世界上最好的语言【呸！啥也不是】
开发环境配置
设置环境变量
如果vs code安装插件下载失败，配置一下go环境变量，设置proxy
go env -w GOPROXY=https://goproxy.io,direct go env -w GO111MODULE=on查看go环境变量
go env所有go的环境变量
set GO111MODULE=on set GOARCH=amd64 set GOPATH=C:\Users\Administrator\go set GOPRIVATE= set GOPROXY=https://goproxy.io,direct set GOROOT=c:\go set GOSUMDB=sum.golang.org ……第一个go web程序
新建main.go
输入helloweb按回车
package main import ( "fmt" "net/http" "time" ) func greet(w http.ResponseWriter, r *http.Request) { fmt.Fprintf(w, "Hello World! %s", time.Now()) } func main() { http.HandleFunc("/", greet) http.ListenAndServe(":8080", nil) }命令行执行go run main.go
然后命令行访问服务
curl http://localhost:8080得到以下的结果，那么第一个golang web就执行成功了
StatusCode : 200 StatusDescription : OK Content : Hello World! 2022-02-09 20:25:07.5051433 +0800 CST m=+55.242234801restful接口定义
导入依赖
go mod init example/web-service-gin产生模块管理文件
module example/web-service-gin go 1.15main.go导入github.com/gin-gonic/gin
import ( "net/http" "github.com/gin-gonic/gin" )执行
go get .go.mod（类似nodejs的package.json)
module example/web-service-gin go 1.15 require github.com/gin-gonic/gin v1.7.7自动扫码导入依赖同时会发现目录产生了go.sum文件，其类似nodejs的package.json.lock文件
github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38= github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38= github.com/gin-contrib/sse v0.1.0 h1:Y/yl/+YNO8GZSjAhjMsSuLt29uWRFHdHYUb5lYOV9qE= github.com/gin-contrib/sse v0.1.0/go.mod h1:RHrZQHXnP2xjPF+u1gW/2HnVO7nvIa9PG3Gm+fLHvGI= github.com/gin-gonic/gin v1.7.7 h1:3DoBmSbJbZAWqXJC3SLjAPfutPJJRN1U5pALB7EeTTs= github.com/gin-gonic/gin v1.7.7/go.mod h1:axIBovoeJpVj8S3BwE0uPMTeReE4+AfFtqpqaZ1qq1U= github.com/go-playground/assert/v2 v2.0.1/go.mod h1:VDjEfimB/XKnb+ZQfWdccd7VUvScMdVu0Titje2rxJ4= ……编写代码
package main import ( "net/http" "github.com/gin-gonic/gin" ) type album struct { ID string `json:"id"` Title string `json:"title"` Artist string `json:"artist"` Price float64 `json:"price"` } var albums = []album{ {ID: "1", Title: "Blue Train", Artist: "John Coltrane", Price: 56.99}, {ID: "2", Title: "Jeru", Artist: "Gerry Mulligan", Price: 17.99}, {ID: "3", Title: "Sarah Vaughan and Clifford Brown", Artist: "Sarah Vaughan", Price: 39.99}, } func getAlbums(ctx *gin.Context) { //返回带缩减的JSON数据 ctx.IndentedJSON(http.StatusOK, albums) } func main() { router := gin.Default() router.GET("/albums", getAlbums)//method:get router.POST("/albums", getAlbums)//method:get router.Run("localhost:8080") }拆分文件
把GetAlbums放到controller,新建controller目录，这也是package的名称，新建albumController.go文件
package controller import ( "example/web-service-gin/models" "net/http" "github.com/gin-gonic/gin" ) func GetAlbums(ctx *gin.Context) { albums := []models.Album{ {ID: "1", Title: "Blue Train", Artist: "John Coltrane", Price: 56.99}, {ID: "2", Title: "Jeru", Artist: "Gerry Mulligan", Price: 17.99}, {ID: "3", Title: "Sarah Vaughan and Clifford Brown", Artist: "Sarah Vaughan", Price: 39.99}, } ctx.IndentedJSON(http.StatusOK, albums) }把Albums结构体独立到models的album.go,go导出方法和结构，都是通过首字母大写的是公开的，其他的不导出，所以album改成Album
package models type Album struct { ID string `json:"id"` Title string `json:"title"` Artist string `json:"artist"` Price float64 `json:"price"` }此时main.go就变成了这样子
package main import ( "example/web-service-gin/controller" "github.com/gin-gonic/gin" ) func main() { router := gin.Default() router.GET("/albums", controller.GetAlbums) router.POST("/albums", controller.GetAlbums) router.Run("localhost:8080") }单元测试
安装依赖
golang的版本有要求，go install 1.15.x的版本没有对go install 的支持，建议升级到最新的版本
go install golang.org/dl/[email protected]单应测试样例
创建test文件夹，创建api_test.go,注意名称要以_test结尾
package test import ( "bytes" "encoding/json" "fmt" "io/ioutil" "net/http" "testing" ) func TestApi(t *testing.T) { res, err := http.Get("http://localhost:8080/albums") if err != nil { panic(err) } //defer 在作用域内最后执行 defer res.Body.Close() result, _ := ioutil.ReadAll(res.Body) fmt.Println(string(result)) } func TestPost(t *testing.T) { data, _ := json.Marshal(struct{ Name, Age string }{}) res, err := http.Post("http://localhost:8080/albums", "application/json", bytes.NewBuffer(data)) if err != nil { panic(err) } defer res.Body.Close() result, _ := ioutil.ReadAll(res.Body) fmt.Println(string(result)) }mysql访问
package db import ( "database/sql" "example/web-service-gin/models" "fmt" "log" "github.com/go-sql-driver/mysql" ) func QueryData () (albumArr []models.Album,queryErr error){ var db *sql.DB; cft :=mysql.Config{ User:"root", Passwd: "123456", Net: "tcp", Addr: "127.0.0.1:3306", DBName: "recodings", AllowNativePasswords:true, } db, err := sql.Open("mysql", cft.FormatDSN()) if err != nil { log.Fatal(err) } pingErr := db.Ping() if pingErr != nil { log.Fatal(pingErr) } fmt.Println("Connected!") rows,dbErr:= db.Query("select * from album"); if(dbErr!=nil){ } defer rows.Close() var albums []models.Album for rows.Next() { var alb models.Album if err := rows.Scan(&alb.ID, &alb.Title, &alb.Artist, &alb.Price); err != nil { return nil, nil } albums = append(albums, alb) } return albums,nil }单元测试
package test import ( "encoding/json" "example/web-service-gin/db" "fmt" "testing" ) func TestDB(t *testing.T) { albums, err := db.QueryData() if err != nil { fmt.Println(err) } data, _ := json.MarshalIndent(albums, "", " ") fmt.Println(string(data)) }得到下面的结果
=== RUN TestDB Connected! [ { "id": "1", "title": "Blue Train", "artist": "John Coltrane", "price": 56.99 }, { "id": "2", "title": "Giant Steps", "artist": "John Coltrane", "price": 63.99 }, { "id": "3", "title": "Jeru", "artist": "Gerry Mulligan", "price": 17.99 }, { "id": "4", "title": "Sarah Vaughan", "artist": "Sarah Vaughan", "price": 34.98 } ] --- PASS: TestDB (0.00s) PASS ok example/web-service-gin/test (cached)接口
接口定义
package interfacedemo import "example/web-service-gin/models" type IAlbumService interface { GetAlbum() []models.Album }实现接口,AlbumService在代码上，不需要引入IAlbumService，只要AlbumService实现了所有的方法即代表AlbumService实现了接口IAlbumService（目前来看，接口没有字段的定义），如果没实现所有的方法编译器将会提示declaration: missing method GetAlbum
package interfacedemo import "example/web-service-gin/models" type AlbumService struct { } func (service *AlbumService) GetAlbum() []models.Album { return []models.Album{{ID: "10", Title: "Blue Train", Artist: "John Coltrane", Price: 100.99}} }调用
package test import ( "encoding/json" "example/web-service-gin/interfacedemo" "example/web-service-gin/models" "fmt" "testing" ) func TestInterface(t *testing.T) { //接口接收实现的实例 var service interfacedemo.IAlbumService =new(interfacedemo.AlbumService) var albums []models.Album = service.GetAlbum() data, _ := json.MarshalIndent(albums, "", " ") fmt.Println("data:", string(data)) }指针
&取址操作，*声明指针类型的变量或者取指针变量指向的值
num := 10 //*声明指针的变量 var numPtr *int = nil //&取num变量的地址 numPtr = &num //*取指针变量numPtr指向的值 ptrValue := *numPtr指针是强类型的，不匹配的类型不能赋值,比如下面的语句就是错误的
var floatPtr *float32=numPtr不过对于struct的赋值，具有隐式转换，比如下面的例子
type IPointer interface{GetPoint()} type Pointer struct {} func (pointer Pointer) GetPoint() {} func main() { var pt *Pointer = new(Pointer) var pt1 IPointer = *point var pt2 IPointer = point var pointer Pointer = Pointer{} var pointer1 IPointer = &pointer var pointer2 IPointer = pointer } 如果是结构体本身，那么不存在隐式转换
var point *Pointer = new(Pointer) var point1 Pointer = *point//正确 var point2 *Pointer = point//正确 var point3 Pointer = point//错误再看下面的例子
package interfacedemo import "example/web-service-gin/models" type IAlbumService interface { GetAlbum() []models.Album }AlbumService和AlbumServiceImpl实现了接口IAlbumService
package interfacedemo import "example/web-service-gin/models" type AlbumService struct {} // 通过AlbumService实现方法GetAlbum，通过该方式实现，指针（隐式转换）和实例均可给接口进行赋值 func (service AlbumService) GetAlbum() []models.Album { return []models.Album{{ID: "10", Title: "Blue Train", Artist: "John Coltrane", Price: 100.99}} } type AlbumServiceImpl struct{} // 通过AlbumServiceImpl的指针类型实现GetAlbum，只能通过指针给接口进行赋值 func (service *AlbumServiceImpl) GetAlbum() []models.Album { return []models.Album{{ID: "10", Title: "Blue Train Impl", Artist: "John Coltrane", Price: 100.99}} }通过以下的方式调用
var service *interfacedemo.AlbumService = new(interfacedemo.AlbumService) var service1 interfacedemo.IAlbumService = service//正确，隐式转换 service1 = *service//正确，AlbumService实例实现了GetAlbum，比较规范的写法 var instance interfacedemo.AlbumService = interfacedemo.AlbumService{} var instance1 interfacedemo.IAlbumService = service//正确，AlbumService实例实现了GetAlbum，比较规范的写法 instance1 = &instance//正确，隐式转换 var serviceImpl interfacedemo.AlbumServiceImpl = interfacedemo.AlbumServiceImpl{} var serviceImpl1 interfacedemo.IAlbumService = &serviceImpl//正确 serviceImpl1 = serviceImpl//错误，AlbumServiceImpl的实例并没有实现GetAlbum var implInstance *interfacedemo.AlbumServiceImpl = new(interfacedemo.AlbumServiceImpl) var implInstance1 interfacedemo.IAlbumService = implInstance//正确 implInstance1 = *implInstance//错误，AlbumServiceImpl的实例并没有实现GetAlbum接口本身声明指针类型是可以的，除了赋值为nil，没办法实例化
var service *interfacedemo.IAlbumService =nil//正确 service = new(interfacedemo.AlbumService)//错误会抛异常：cannot use new(interfacedemo.AlbumService) (value of type *interfacedemo.AlbumService) as *interfacedemo.IAlbumService value in assignment
golang的指针类型跟C++的有所不同
type Pointer struct {} func main() { var instance Pointer = Pointer{} fmt.Println(instance,instancePtr,&instancePtr) }得到的结果是
{} &{} 0xc000006028&instance并不是得到一个地址，更像一个表示对instance取址的操作，&instancePtr则是instancePtr的地址，也就是指针的指针
那如果输出修改成
fmt.Println(instance,&instance,&(&instance))&(&instance)编译器报错：invalid operation: cannot take address of (&instance) (value of type *Pointer)
&instancePtr与&(&instance)不相同，&(&instance)这样并没有给指向&instance分配地址
值得注意的是golang的结构体是值类型的，如果需要修改结构体的字段的值，需要用指针，下面来看一下这个例子
package main import ( "fmt" ) type Vertex struct { X, Y int } func changeVertex(ver Vertex) { ver.X = 100 ver.Y = 100 } func changeVertexByPointer(ver *Vertex) { (*ver).X = 100//*号优先级是低于.的，所以要加上(),当然，直接ver.X也是可以的 ver.Y = 100 } func main() { ver := Vertex{X: 10, Y: 10} changeVertex(ver) fmt.Println(ver.X, ver.Y) changeVertexByPointer(&ver) fmt.Println(ver.X, ver.Y) }得到的结果是
10 10 100 100换一种写法
package main import ( "fmt" ) type Vertex struct { X, Y int } func (ver Vertex) changeVertex() { ver.X = 100 ver.Y = 100 } func (ver *Vertex) changeVertexByPointer() { (*ver).X = 100 ver.Y = 100 } func main() { //实例调用 ver := Vertex{X: 10, Y: 10} ver.changeVertex() fmt.Println(ver.X, ver.Y) //指针调用 (&ver).changeVertexByPointer() fmt.Println(ver.X, ver.Y) }通常情况下，建议使用指针，除非为了要避免修改原来实例的值。
值传递，尤其是复杂的结构体，会做拷贝处理，使用指针性能相对会更好。
接口实例化
package main import ( "fmt" ) type Vertex struct { X, Y int } type IVertex interface { GetResult() int } func (ver Vertex) GetResult() int { var result int=ver.X + ver.Y fmt.Println("result:",result) return result } func main() { var iv IVertex //iv.GetResult()//这一句会在运行时抛异常：panic: runtime error: invalid memory address or nil pointer dereference var v Vertex iv = v fmt.Println(iv,v)//打印{0 0}{0 0} iv.GetResult()//结果是0 iv = Vertex{X: 10, Y: 10} iv.GetResult()//结果20 }接口类型判断
var typeVar interface{} = "hello" t, result := typeVar.(string) fmt.Println(t, result)// hello truetypeVar.(string)如果类型是对的，第二个参数可以不写，得到的是实际的值，如果类型不正确,比如t:=typeVar.(string)，将会抛异常interface conversion: interface {} is string, not int,如果t,result:=typeVar.(string)，t则是0，result是false
switch case类型
var typeVar interface{} = nil switch t := typeVar.(type) { case int: fmt.Println("int:", t) default: fmt.Printf("%T", t) }切片
在了解切片之前，先来看看数组，切片是基于数组定义的。
package main import "fmt" func main() { arr:=[6]int{1,2,3,4,5,6} fmt.Println(arr); }数组是个定长的，如果初始化的元素个数少于6个，那么会自动补上零值，多于6个会提示越界
数组完整的声明写法
var arr [6]int=[6]int{1,2,3,4,5,6}那么切片是什么？切片是基于对数组的引用,slice是个结构体，注意slice本身是值传递的
type slice struct { array unsafe.Pointer len int cap int//默认容量于len相等 }从这里可以看出，切片修改元素，那么对应的数组的值也跟着修改，多个基于这个数组的切片修改同一个元素，全部都会被修改，下面来看看以下的例子
package main import "fmt" func main() { var arr [6]int=[6]int{1,2,3,4,5} sliceA:=arr[:] sliceB:=arr[1:3] sliceA[1]=10 fmt.Println(sliceB[0])//10 fmt.Println(arr[1])//10 }切片的一些操作
package main import "fmt" func main() { var arr [6]int = [6]int{1, 2, 3, 4, 5, 6} // 声明切片，arr[:3:5]，第一个不写那么值是0，第二个是截取到第（下标-1）的元素，第三个是初始的容量，不写默认是数组的长度，不允许超过数组的长度 slice := arr[:3:5] fmt.Println(slice, cap(slice), len(slice))//[1 2 3] 5 3 slice = append(slice, 10)//在末尾添加元素，返回一个新的切片 slice = append(slice, 20) slice = append(slice, 30) fmt.Println(slice, cap(slice), len(slice))// [1 2 3 10 20 30] 10 6 长度用完，自动扩容 }映射
go的映射实际就是java的map或者是c#的dictionary，定义是map[keyType]valueType
package main import ( "fmt" ) func main() { var maps map[string]int = map[string]int{ "tome": 20, "kate": 18, "tub": 45, } for key, value := range maps { fmt.Println(key, value) } }map的一些操作
package main import ( "fmt" ) func main() { // 初始化 var maps Map = Map{ "tome": 20, "kate": 18, "tub": 45, } // 存在的key修改 maps["tome"]=33 // 不存在的key新增 maps["heihei"]=43 // 判断是否包含key value,exists:=maps["join"] fmt.Println("join is exists:",value,exists)//value是零值 value,exists =maps["kate"] fmt.Println("kate is exists:",value,exists)//value对应的是key为kate对应的值 for key, value := range maps { fmt.Println(key, value) } fmt.Println("=====================") delete(maps,"heihei") for key, value := range maps { fmt.Println(key, value) } }结果
join is exists: 0 false kate is exists: 18 true kate 18 tub 45 heihei 43 tome 33 ===================== tome 33 kate 18 tub 45泛型
1.18之前的版本是不支持泛型的，beta1开始新增了对泛型的支持
type Number interface {//类似c#里做了泛型约束 int64 | float64 }比如数字相加
package main import "fmt" func main() { intResult:= Add[int](1,1) floatResult := Add[float64](1.1,1.1) fmt.Println("1 + 1 =",intResult) fmt.Println("1.1 + 1.1 =",floatResult) } func Add[T int|float64](num1 T,num2 T) T{ return num1+num2 }得到
1 + 1 = 2 1.1 + 1.1 = 2.1泛型类型实际是个接口类型，比如上面的例子可以这样写
package main import "fmt" type Number interface{ int|float64 } func main() { intResult:= Add[int](1,1) floatResult := Add[float64](1.1,1.1) fmt.Println("1 + 1 =",intResult) fmt.Println("1.1 + 1.1 =",floatResult) } // Number 替代了int|float64 func Add[T Number](num1 T,num2 T) T{ return num1+num2 }这种定义方式实际是限定了泛型的类型，必须显示指出泛型的类型组合。
下面来自定义接口
package main import "fmt" type IService interface{ GetServiceName() string } type ServiceT interface{ IService } type UserService struct{Name string} func (service UserService) GetServiceName() string{ return service.Name } type RoleService struct{Name string} func (service RoleService) GetServiceName() string{ return service.Name } func GetService[ST ServiceT](serviceType ST) string{ return serviceType.GetServiceName() } func main() { serviceName:= GetService[UserService](UserService{Name: "userService"}) fmt.Println("服务名称:",serviceName) serviceName= GetService[RoleService](RoleService{Name: "roleService"}) fmt.Println("服务名称:",serviceName) }得到
服务名称: userService 服务名称: roleService那ServiceT改成空接口，是否能够调用？目前的版本（1.18beta2）是不支持的
type ServiceT interface{}ServiceT是空接口会提示.\gen.go:41:14: serviceType.GetServiceName undefined (type ST has no field or method GetServiceName)
那我们通过反射来看看是否能够找到GetServiceName?
func GetService[ST ServiceT](serviceType ST) string{ t:= reflect.TypeOf(serviceType)//获取类型 v:=reflect.ValueOf(serviceType)//获取值 methodCount:= t.NumMethod() for i := 0; i < methodCount; i++ { methodName:=t.Method(i).Name fmt.Println(methodName) val:= v.MethodByName(methodName).Call(nil) //调用方法 return val[0].String()//把reflect.value转换为string类型 } return "" }得到输出
GetServiceName 服务名称: userService GetServiceName 服务名称: roleServicego程
go程是开启了一个线程，如果主进程结束，那么开启的go程也会跟着结束
package main import ( "fmt" "time" ) func say(s string,count int) { for i := 0; i < count; i++ { time.Sleep(100 * time.Millisecond) fmt.Println(s) } } func main() { go say("world",10) say("hello",3) }输出结果
hello world world hello hello可以看到，当hello输出3次，主进程结束，那么通过go say("world",10)调用的并没有执行完，也跟着结束了
channel
发送和接收操作在另一端准备好之前都会阻塞
信道上的发送操作总在对应的接收操作完成前发生。
若在信道关闭后从中接收数据，接收者就会收到该信道返回的零值。
从无缓冲信道进行的接收，要发生在对该信道进行的发送完成之前。
select
package main import ( "fmt" "time" ) func main() { //<-chan time.Time表示该channel只能发送 var tick <-chan time.Time = time.Tick(100 * time.Millisecond) boom := time.After(500 * time.Millisecond) for { select { case <-tick: fmt.Println("tick") case <-boom: fmt.Println("boom!") return default: fmt.Println("……") time.Sleep(50 * time.Millisecond) } } }单向channel
package main import ( "fmt" "time" ) //ch只能接收 func receive(ch chan<- string, str string) { ch <- str } //sender只能发送，receiver只能接收 func send(sender <-chan string, receiver chan<- string) { time.Sleep(time.Second) receiver <- <-sender } func main() { var sender chan string = make(chan string) var receiver chan string = make(chan string) go receive(sender, "hi,let's go") go send(sender, receiver) str := <-receiver fmt.Println(str)//输出：hi,let's go }缓冲通道
package main import ( "fmt" ) func main() { var ch chan string = make(chan string) ch <- "hello" str := <-ch fmt.Println(str) }以上的代码会抛出异常：fatal error: all goroutines are asleep – deadlock!
发送和接收操作在另一端准备好之前都会阻塞，这时候，无缓冲的通道，会造成死锁
package main import ( "fmt" ) func main() { var ch chan string = make(chan string,1) ch <- "hello" str := <-ch fmt.Println(str) }