浅析golang的依赖注入

type Config struct {
        Prefix string
}

//初始化Config函数
func NewConfig()(*Config, error) {
        // In a real program, the configuration will probably be read from a
        // file.
        var cfg Config
        err := json.Unmarshal([]byte(`{"prefix": "[foo] "}`), &cfg)
        return &cfg, err
}

//初始化logger函数
func NewLogger(cfg *Config) *log.Logger {
    return log.New(os.Stdout, cfg.Prefix, 0)
}

func Handle() (l *log.Logger) {
    l.Print("You've been invoked")
}

func main() {
    //初始化dig对象
    c := dig.New()

    //Provide方法用来设置依赖的对象
    er := c.Provide(NewConfig)
    if err != nil {
        panic(err)
    }

    //设置依赖的对象
    err = c.Provide(NewLogger)
    if err != nil {
        panic(err)
    }
    
    //执行Handle()方法
    //Handle依赖 Config 和 Logger，使用Invoke执行方法时会自动注入依赖（依赖的对象要传入Provide方法中）
    err = c.Invoke(Handle)
    if err != nil {
        panic(err)
    }
    // Output:
    // [foo] You've been invoked
}

// +build wireinject

package main

import (
    "encoding/json"
    "fmt"
    "github.com/google/wire"
    "net/http"
)

type DataSource struct {
    Operation string
}

func NewDataSource() DataSource {
    return DataSource{Operation: "operation_name"}
}

//==================

type Dao struct {
    DataSource DataSource
}

func NewDao(ds DataSource) *Dao {
    return &Dao{
        DataSource: ds,
    }
}

func (d *Dao) GetItemList() ([]string, error) {
    //TODO 拿到DB对象做查询操作
    fmt.Printf("db object: %s", d.DataSource.Operation)
    return []string{d.DataSource.Operation, "item1", "item2"}, nil
}

//====================

type Service struct {
    Dao *Dao
}

func NewService(dao *Dao) *Service {
    return &Service{Dao: dao}
}

func (s *Service) GetItemList() ([]string, error) {
    return s.Dao.GetItemList()
}

//=====================

type Controller struct {
    Service *Service
}

func NewController(service *Service) *Controller {
    return &Controller{Service: service}
}

func (c *Controller) GetItemList() ([]string, error) {
    return c.Service.GetItemList()
}

var MegaSet = wire.NewSet(NewDataSource, NewDao, NewService, NewController)

func initializeController() *Controller {
    wire.Build(MegaSet)
    return &Controller{}
}

func getItemList(w http.ResponseWriter, r *http.Request) {
    controller := initializeController()
    itemList, _ := controller.GetItemList()
    output, _ := json.Marshal(itemList)
    fmt.Fprintf(w, string(output))
}

func main() {
    http.HandleFunc("/items", getItemList)
    err := http.ListenAndServe(":8080", nil)
    if err != nil {
        panic(err)
    }
}

// Code generated by Wire. DO NOT EDIT.

//go:generate go run github.com/google/wire/cmd/wire
//+build !wireinject

package main

import (
    "encoding/json"
    "fmt"
    "github.com/google/wire"
    "net/http"
)

// Injectors from main.go:
// 此处是生成的代码
func initializeController() *Controller {
    dataSource := NewDataSource()
    dao := NewDao(dataSource)
    service := NewService(dao)
    controller := NewController(service)
    return controller
}

// main.go:

type DataSource struct {
    Operation string
}

func NewDataSource() DataSource {
    return DataSource{Operation: "operation_name"}
}

type Dao struct {
    DataSource DataSource
}

func NewDao(ds DataSource) *Dao {
    return &Dao{
        DataSource: ds,
    }
}

func (d *Dao) GetItemList() ([]string, error) {
    fmt.Printf("db object: %s", d.DataSource.Operation)
    return []string{d.DataSource.Operation, "item1", "item2"}, nil
}

type Service struct {
    Dao *Dao
}

func NewService(dao *Dao) *Service {
    return &Service{Dao: dao}
}

func (s *Service) GetItemList() ([]string, error) {
    return s.Dao.GetItemList()
}

type Controller struct {
    Service *Service
}

func NewController(service *Service) *Controller {
    return &Controller{Service: service}
}

func (c *Controller) GetItemList() ([]string, error) {
    return c.Service.GetItemList()
}

var MegaSet = wire.NewSet(NewDataSource, NewDao, NewService, NewController)

func getItemList(w http.ResponseWriter, r *http.Request) {
    controller := initializeController()
    itemList, _ := controller.GetItemList()
    output, _ := json.Marshal(itemList)
    fmt.Fprintf(w, string(output))
}

func main() {
    http.HandleFunc("/items", getItemList)
    err := http.ListenAndServe(":8080", nil)
    if err != nil {
        panic(err)
    }
}

//执行wire命令前的代码
func initializeController() *Controller {
    wire.Build(MegaSet)
    return &Controller{}
}

//执行后生成的代码
// Injectors from main.go:
func initializeController() *Controller {
    dataSource := NewDataSource()
    dao := NewDao(dataSource)
    service := NewService(dao)
    controller := NewController(service)
    return controller
}