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=+55.242234801

restful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 1.15

main.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/go1.18beta1@latest

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 true

typeVar.(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: roleService

go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)
}