var injectTagName = "inject" //依赖注入tag名

//生命周期
// singleton：单例 单一实例，每次使用都是该实例
// transient:瞬时实例,每次使用都创建新的实例
type Container struct {
    sync.Mutex
    singletons map[string]interface{}
    transients map[string]factory
}

type factory = func() (interface{}, error)

//注册单例对象
func (c *Container) SetSingleton(name string, singleton interface{}) {
    c.Lock()
    c.singletons[name] = singleton
    c.Unlock()
}

func (c *Container) GetSingleton(name string) interface{} {
    return c.singletons[name]
}

//注册瞬时实例创建工厂方法
func (c *Container) SetTransient(name string, factory factory) {
    c.Lock()
    c.transients[name] = factory
    c.Unlock()
}

func (c *Container) GetTransient(name string) interface{} {
    factory := c.transients[name]
    instance, _ := factory()
    return instance
}

//注入实例
func (c *Container) Entry(instance interface{}) error {
    err := c.entryValue(reflect.ValueOf(instance))
    if err != nil {
        return err
    }
    return nil
}

func (c *Container) entryValue(value reflect.Value) error {
    if value.Kind() != reflect.Ptr {
        return errors.New("必须为指针")
    }
    elemType, elemValue := value.Type().Elem(), value.Elem()
    for i := 0; i < elemType.NumField(); i++ {
        if !elemValue.Field(i).CanSet() { //不可设置 跳过
            continue
        }

        fieldType := elemType.Field(i)
        if fieldType.Anonymous {
            //fmt.Println(fieldType.Name + "是匿名字段")
            item := reflect.New(elemValue.Field(i).Type())
            c.entryValue(item) //递归注入
            elemValue.Field(i).Set(item.Elem())
        } else {
            if elemValue.Field(i).IsZero() { //零值才注入
                //fmt.Println(elemValue.Field(i).Interface())
                //fmt.Println(fieldType.Name)
                tag := fieldType.Tag.Get(injectTagName)
                injectInstance, err := c.getInstance(tag)
                if err != nil {
                    return err
                }
                c.entryValue(reflect.ValueOf(injectInstance)) //递归注入

                elemValue.Field(i).Set(reflect.ValueOf(injectInstance))
            } else {
                fmt.Println(fieldType.Name)
            }
        }
    }
    return nil
}

func (c *Container) getInstance(tag string) (interface{}, error) {
    var injectName string
    tags := strings.Split(tag, ",")
    if len(tags) == 0 {
        injectName = ""
    } else {
        injectName = tags[0]
    }

    if c.isTransient(tag) {
        factory, ok := c.transients[injectName]
        if !ok {
            return nil, errors.New("transient factory not found")
        } else {
            return factory()
        }
    } else { //默认单例
        instance, ok := c.singletons[injectName]
        if !ok || instance == nil {
            return nil, errors.New(injectName + " dependency not found")
        } else {
            return instance, nil
        }
    }
}

// transient:瞬时实例,每次使用都创建新的实例
func (c *Container) isTransient(tag string) bool {
    tags := strings.Split(tag, ",")
    for _, name := range tags {
        if name == "transient" {
            return true
        }
    }
    return false
}

func (c *Container) String() string {
    lines := make([]string, 0, len(c.singletons)+len(c.transients)+2)
    lines = append(lines, "singletons:")
    for key, value := range c.singletons {
        line := fmt.Sprintf("    %s: %x %s", key, c.singletons[key], reflect.TypeOf(value).String())
        lines = append(lines, line)
    }

    lines = append(lines, "transients:")
    for key, value := range c.transients {
        line := fmt.Sprintf("    %s: %x %s", key, c.transients[key], reflect.TypeOf(value).String())
        lines = append(lines, line)
    }
    return strings.Join(lines, "
")
}

这里使用了两种生命周期的实例：单例和瞬时（其他生命周期，水平有限哈）

简单说下原理，容器主要包含两个map对象，用来存储对象和创建对方方法，然后依赖注入实现，就是通过反射获取tag信息，再去容器map中获取对象，通过反射把获取的对象赋值到字段中。

我这里采用了递归注入的方式，所以本项目中，只用注入UserController对象即可，因为实际项目中多点是有多个Controller对象，所以我这里使用了个简单工厂来创建Controller对象，然后只用注入工厂方法即可

工厂方法实现如下：

type CtrlFactory struct {
    UserCtrl *controllers.UserController `inject:"UserController"`
}

var GContainer = &Container{
    singletons: make(map[string]interface{}),
    transients: make(map[string]factory),
}

func Init() {
    //db
    GContainer.SetSingleton("MockDBRead", &db.MockDB{Host: "192.168.1.12:3036", User: "root", Pwd: "123456", Alias: "Read"})
    GContainer.SetSingleton("MockDBWrite", &db.MockDB{Host: "192.168.1.25:3036", User: "root", Pwd: "123456", Alias: "Write"})

    //仓储
    GContainer.SetSingleton("UserRepository", &user.UserRepository{})

    //服务
    GContainer.SetSingleton("UserService", &userDomain.UserService{})

    //控制器
    GContainer.SetSingleton("UserController", &controllers.UserController{})

    //控制器工厂
    ctlFactory := &CtrlFactory{}
    GContainer.SetSingleton("CtrlFactory", ctlFactory)

    GContainer.Entry(ctlFactory) //注入

    fmt.Println(GContainer.String())
}

func main() {
    Init()
    Run()
}

func Init() {
    inject.Init()
}

func Run() {
    router := router.Init()

    s := &http.Server{
        Addr:           ":8080",
        Handler:        router,
        ReadTimeout:    time.Duration(10) * time.Second,
        WriteTimeout:   time.Duration(10) * time.Second,
        MaxHeaderBytes: 1 << 20,
    }
    go func() {
        log.Println("Server Listen at:8080")
        if err := s.ListenAndServe(); err != nil {
            log.Printf("Listen:%s
", err)
        }
    }()

    quit := make(chan os.Signal)
    signal.Notify(quit, os.Interrupt)
    <-quit

    log.Println("Shutdown Server...")
    ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
    defer cancel()
    if err := s.Shutdown(ctx); err != nil {
        log.Fatal("Server Shutdown:", err)
    }
    log.Println("Server exiting")
}

func Init() *gin.Engine {
    // Creates a router without any middleware by default
    r := gin.New()
    r.Use(gin.Logger())
    // Recovery middleware recovers from any panics and writes a 500 if there was one.
    r.Use(gin.Recovery())

    r.GET("/ping", func(c *gin.Context) {
        c.JSON(200, gin.H{
            "message": "pong",
        })
    })

    factory := inject.GContainer.GetSingleton("CtrlFactory")
    ctrlFactory := factory.(*inject.CtrlFactory)

    apiV1 := r.Group("/api/v1")
    //users
    userRg := apiV1.Group("/user")
    {
        userRg.POST("", ctrlFactory.UserCtrl.AddUser)
        userRg.GET("", ctrlFactory.UserCtrl.GetUsers)
        userRg.GET("/:id", ctrlFactory.UserCtrl.GetUser)
    }

    gin.SetMode("debug")
    return r
}

factory := inject.GContainer.GetSingleton("CtrlFactory")
ctrlFactory := factory.(*inject.CtrlFactory)