手撸golang 结构型设计模式 门面模式
2009 年 9 月 26 日
手撸golang 结构型设计模式 门面模式
缘起
最近复习设计模式
拜读谭勇德的<<设计模式就该这样学>>
本系列笔记拟采用golang练习之
门面模式
门面模式(Facade Pattern)又叫作外观模式,提供了一个统一的接口,用来访问子系统中的一群接口。其主要特征是定义了一个高层接口,让子系统更容易使用,属于结构型设计模式。
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场景
- 某在线商城, 推出了积分兑换礼品的功能
- 兑换礼品有几个步骤, 涉及到若干子系统:
- 积分系统, 检查用户积分是否足够
- 库存系统, 检查礼品是否有库存
- 物流系统, 安排礼品发货并生成发货订单
- 为简化业务层接口, 以门面模式设计统一的积分兑换API接口 – IGiftExchangeService
设计
- GiftInfo: 礼品信息实体. 礼品也是一种库存物品.
- GiftExchangeRequest: 积分兑换礼品申请
- IGiftExchangeService: 积分兑换礼品服务, 该服务是一个Facade, 内部调用了多个子系统的服务
- IPointsService: 用户积分管理服务的接口
- IInventoryService: 库存管理服务的接口
- IShippingService: 物流下单服务的接口
- tMockGiftExchangeService: 积分兑换礼品服务的实现类
- tMockPointsService: 用户积分管理服务的实现类
- tMockInventoryService: 库存管理服务的实现类
- tMockShippingService: 物流下单服务的实现类
单元测试
facade_pattern_test.go
package structural_patterns import ( "learning/gooop/structural_patterns/facade" "testing" "time" ) func Test_FacadePattern(t *testing.T) { iUserID := 1 iGiftID := 2 // 预先存入1000积分 e := facade.MockPointsService.SaveUserPoints(iUserID, 1000) if e != nil { t.Error(e) return } // 预先存入1个库存 e = facade.MockInventoryService.SaveStock(iGiftID, 1) if e != nil { t.Error(e) return } request := &facade.GiftExchangeRequest{ ID: 1, UserID: iUserID, GiftID: iGiftID, CreateTime: time.Now().Unix(), } e, sOrderNo := facade.MockGiftExchangeService.Exchange(request) if e != nil { t.Log(e) } t.Logf("shipping order no = %v", sOrderNo) }
测试输出
$ go test -v facade_pattern_test.go === RUN Test_FacadePattern facade_pattern_test.go:36: shipping order no = shipping-order-666 --- PASS: Test_FacadePattern (0.00s) PASS ok command-line-arguments 0.002s
GiftInfo.go
礼品信息实体
package facade type GiftInfo struct { ID int Name string Points int } func NewGiftInfo(id int, name string, points int) *GiftInfo { return &GiftInfo{ id, name, points, } }
GiftExchangeRequest.go
积分兑换礼品请求
package facade type GiftExchangeRequest struct { ID int UserID int GiftID int CreateTime int64 }
IGiftExchangeService.go
积分兑换礼品的接口, 该接口是为方便客户端调用的Facade接口
package facade // 礼品兑换服务 type IGiftExchangeService interface { // 兑换礼品, 并返回物流单号 Exchange(request *GiftExchangeRequest) (error, string) }
IPointsService.go
模拟用户积分管理服务的接口
package facade // 用户积分服务 type IPointsService interface { GetUserPoints(uid int) (error, int) SaveUserPoints(uid int, points int) error }
IInventoryService.go
模拟库存管理服务的接口
package facade // 库存服务 type IInventoryService interface { GetGift(goodsID int) *GiftInfo GetStock(goodsID int) (error, int) SaveStock(goodsID int, num int) error }
IShippingService.go
模拟物流下单服务的接口
package facade // 物流下单服务 type IShippingService interface { CreateShippingOrder(uid int, goodsID int) (error, string) }
tMockGiftExchangeService.go
实现积分兑换礼品服务. 内部封装了积分服务, 库存服务和物流下单服务的调用.
package facade import "errors" type tMockGiftExchangeService struct { } func newMockGiftExchangeService() IGiftExchangeService { return &tMockGiftExchangeService{} } var MockGiftExchangeService = newMockGiftExchangeService() // 模拟环境下未考虑事务提交和回滚 func (me *tMockGiftExchangeService) Exchange(request *GiftExchangeRequest) (error, string) { gift := MockInventoryService.GetGift(request.GiftID) if gift == nil { return errors.New("gift not found"), "" } e, points := MockPointsService.GetUserPoints(request.UserID) if e != nil { return e, "" } if points < gift.Points { return errors.New("insufficient user points"), "" } e, stock := MockInventoryService.GetStock(gift.ID) if e != nil { return e, "" } if stock <= 0 { return errors.New("insufficient gift stock"), "" } e = MockInventoryService.SaveStock(gift.ID, stock-1) if e != nil { return e, "" } e = MockPointsService.SaveUserPoints(request.UserID, points - gift.Points) if e != nil { return e, "" } e,orderNo := MockShippingService.CreateShippingOrder(request.UserID, gift.ID) if e != nil { return e, "" } return nil, orderNo }
tMockPointsService.go
���拟实现用户积分管理服务
package facade import "errors" var MockPointsService = newMockPointsService() type tMockPointsService struct { mUserPoints map[int]int } func newMockPointsService() IPointsService { return &tMockPointsService{ make(map[int]int, 16), } } func (me *tMockPointsService) GetUserPoints(uid int) (error, int) { n,ok := me.mUserPoints[uid] if ok { return nil, n } else { return errors.New("user not found"), 0 } } func (me *tMockPointsService) SaveUserPoints(uid int, points int) error { me.mUserPoints[uid] = points return nil }
tMockInventoryService.go
模拟实现库存管理服务
package facade var MockInventoryService = newMockInventoryService() type tMockInventoryService struct { mGoodsStock map[int]int } func newMockInventoryService() IInventoryService { return &tMockInventoryService{ make(map[int]int, 16), } } func (me *tMockInventoryService) GetGift(id int) *GiftInfo { return NewGiftInfo(id, "mock gift", 100) } func (me *tMockInventoryService) GetStock(goodsID int) (error, int) { n,ok := me.mGoodsStock[goodsID] if ok { return nil, n } else { return nil, 0 } } func (me *tMockInventoryService) SaveStock(goodsID int, num int) error { me.mGoodsStock[goodsID] = num return nil }
tMockShippingService.go
模拟实现物流下单服务
package facade var MockShippingService = newMockShippingService() type tMockShippingService struct { } func newMockShippingService() IShippingService { return &tMockShippingService{} } func (me *tMockShippingService) CreateShippingOrder(uid int, goodsID int) (error, string) { return nil, "shipping-order-666" }
门面模式小结
门面模式的优点
(1)简化了调用过程,不用深入了解子系统,以防给子系统带来风险。
(2)减少系统依赖,松散耦合。
(3)更好地划分访问层次,提高了安全性。
(4)遵循迪米特法则
门面模式的缺点
(1)当增加子系统和扩展子系统行为时,可能容易带来未知风险。
(2)不符合开闭原则。
(3)某些情况下,可能违背单一职责原则。
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