Go 设计模式 - 工厂模式

简单工厂模式

go 语言没有构造函数一说，所以一般会定义NewXXX函数来初始化相关类。
NewXXX 函数返回接口时就是简单工厂模式，也就是说Golang的一般推荐做法就是简单工厂。

在这个simplefactory包中只有API 接口和NewAPI函数为包外可见，封装了实现细节。

simple.go代码

package simplefactory

import "fmt"

//API is interface
type API interface {
    Say(name string) string
}

//NewAPI return Api instance by type
func NewAPI(t int) API {
    if t == 1 {
        return &hiAPI{}
    } else if t == 2 {
        return &helloAPI{}
    }
    return nil
}

//hiAPI is one of API implement
type hiAPI struct{}

//Say hi to name
func (*hiAPI) Say(name string) string {
    return fmt.Sprintf("Hi, %s", name)
}

//HelloAPI is another API implement
type helloAPI struct{}

//Say hello to name
func (*helloAPI) Say(name string) string {
    return fmt.Sprintf("Hello, %s", name)
}

　　

simple_test.go代码

package simplefactory

import "testing"

//TestType1 test get hiapi with factory
func TestType1(t *testing.T) {
    api := NewAPI(1)
    s := api.Say("Tom")
    if s != "Hi, Tom" {
        t.Fatal("Type1 test fail")
    }
}

func TestType2(t *testing.T) {
    api := NewAPI(2)
    s := api.Say("Tom")
    if s != "Hello, Tom" {
        t.Fatal("Type2 test fail")
    }
}

　　

工厂方法模式

工厂方法模式使用子类的方式延迟生成对象到子类中实现。

Go中不存在继承 所以使用匿名组合来实现

factorymethod.go

package factorymethod

//Operator 是被封装的实际类接口
type Operator interface {
    SetA(int)
    SetB(int)
    Result() int
}

//OperatorFactory 是工厂接口
type OperatorFactory interface {
    Create() Operator
}

//OperatorBase 是Operator 接口实现的基类，封装公用方法
type OperatorBase struct {
    a, b int
}

//SetA 设置 A
func (o *OperatorBase) SetA(a int) {
    o.a = a
}

//SetB 设置 B
func (o *OperatorBase) SetB(b int) {
    o.b = b
}

//PlusOperatorFactory 是 PlusOperator 的工厂类
type PlusOperatorFactory struct{}

func (PlusOperatorFactory) Create() Operator {
    return &PlusOperator{
        OperatorBase: &OperatorBase{},
    }
}

//PlusOperator Operator 的实际加法实现
type PlusOperator struct {
    *OperatorBase
}

//Result 获取结果
func (o PlusOperator) Result() int {
    return o.a + o.b
}

//MinusOperatorFactory 是 MinusOperator 的工厂类
type MinusOperatorFactory struct{}

func (MinusOperatorFactory) Create() Operator {
    return &MinusOperator{
        OperatorBase: &OperatorBase{},
    }
}

//MinusOperator Operator 的实际减法实现
type MinusOperator struct {
    *OperatorBase
}

//Result 获取结果
func (o MinusOperator) Result() int {
    return o.a - o.b
}

factorymethod_test.go

package factorymethod

import "testing"

func compute(factory OperatorFactory, a, b int) int {
    op := factory.Create()
    op.SetA(a)
    op.SetB(b)
    return op.Result()
}

func TestOperator(t *testing.T) {
    var (
        factory OperatorFactory
    )

    factory = PlusOperatorFactory{}
    if compute(factory, 1, 2) != 3 {
        t.Fatal("error with factory method pattern")
    }

    factory = MinusOperatorFactory{}
    if compute(factory, 4, 2) != 2 {
        t.Fatal("error with factory method pattern")
    }
}

　　

 创建者模式

将一个复杂对象的构建分离成多个简单对象的构建组合

builder.go

package builder

//Builder 是生成器接口
type Builder interface {
    Part1()
    Part2()
    Part3()
}

type Director struct {
    builder Builder
}

// NewDirector ...
func NewDirector(builder Builder) *Director {
    return &Director{
        builder: builder,
    }
}

//Construct Product
func (d *Director) Construct() {
    d.builder.Part1()
    d.builder.Part2()
    d.builder.Part3()
}

type Builder1 struct {
    result string
}

func (b *Builder1) Part1() {
    b.result += "1"
}

func (b *Builder1) Part2() {
    b.result += "2"
}

func (b *Builder1) Part3() {
    b.result += "3"
}

func (b *Builder1) GetResult() string {
    return b.result
}

type Builder2 struct {
    result int
}

func (b *Builder2) Part1() {
    b.result += 1
}

func (b *Builder2) Part2() {
    b.result += 2
}

func (b *Builder2) Part3() {
    b.result += 3
}

func (b *Builder2) GetResult() int {
    return b.result
}

builder_test.go

package builder

import "testing"

func TestBuilder1(t *testing.T) {
    builder := &Builder1{}
    director := NewDirector(builder)
    director.Construct()
    res := builder.GetResult()
    if res != "123" {
        t.Fatalf("Builder1 fail expect 123 acture %s", res)
    }
}

func TestBuilder2(t *testing.T) {
    builder := &Builder2{}
    director := NewDirector(builder)
    director.Construct()
    res := builder.GetResult()
    if res != 6 {
        t.Fatalf("Builder2 fail expect 6 acture %d", res)
    }
}

 

 单例模式

使用懒惰模式的单例模式，使用双重检查加锁保证线程安全

singleton.go

package singleton

import "sync"

//Singleton 是单例模式类
type Singleton struct{}

var singleton *Singleton
var once sync.Once

//GetInstance 用于获取单例模式对象
func GetInstance() *Singleton {
    once.Do(func() {
        singleton = &Singleton{}
    })

    return singleton
}

singleton_test.go

 

package singleton

import (
    "sync"
    "testing"
)

const parCount = 100

func TestSingleton(t *testing.T) {
    ins1 := GetInstance()
    ins2 := GetInstance()
    if ins1 != ins2 {
        t.Fatal("instance is not equal")
    }
}

func TestParallelSingleton(t *testing.T) {
    wg := sync.WaitGroup{}
    wg.Add(parCount)
    instances := [parCount]*Singleton{}
    for i := 0; i < parCount; i++ {
        go func(index int) {
            instances[index] = GetInstance()
            wg.Done()
        }(i)
    }
    wg.Wait()
    for i := 1; i < parCount; i++ {
        if instances[i] != instances[i-1] {
            t.Fatal("instance is not equal")
        }
    }
}