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外观模式：复杂系统的统一入口

news 2025/11/1 22:23:28

在软件开发中，我们经常会遇到需要与复杂子系统交互的场景。外观模式通过提供一个统一的简化接口，隐藏系统的复杂性，让客户端能够更轻松地使用系统功能。

什么是外观模式？

外观模式（Facade Pattern）是一种结构型设计模式，它为复杂的子系统提供一个统一的简化接口。这个模式遵循"最少知识原则"，让客户端只需要与一个高层接口交互，而不需要了解底层系统的复杂性。

就像现实世界中的酒店前台：客人不需要直接与客房服务、餐厅、保洁等多个部门打交道，只需要通过前台就能获得所有服务。

核心概念

外观（Facade）：提供简化的统一接口
子系统（Subsystem）：由多个相互关联的类组成的复杂系统
客户端（Client）：通过外观接口与系统交互

实战案例：智能家居控制系统

让我们通过一个完整的智能家居系统来理解外观模式的实际应用。

1. 定义子系统组件

// 灯光子系统
class LightingSystem {private val lights = mutableMapOf("living_room" to false,"bedroom" to false,"kitchen" to false)fun turnOn(light: String) {lights[light] = trueprintln("💡 $light 灯光已打开")}fun turnOff(light: String) {lights[light] = falseprintln("💡 $light 灯光已关闭")}fun dim(light: String, level: Int) {println("💡 $light 灯光调至 $level%")}fun getStatus(): Map<String, Boolean> {return lights.toMap()}
}// 空调子系统
class AirConditioningSystem {private var isOn = falseprivate var temperature = 26.0private var mode = "cool" // cool, heat, fanfun turnOn() {isOn = trueprintln("❄️ 空调已开启，温度: ${temperature}℃，模式: $mode")}fun turnOff() {isOn = falseprintln("❄️ 空调已关闭")}fun setTemperature(temp: Double) {temperature = tempif (isOn) {println("❄️ 空调温度设置为 ${temp}℃")}}fun setMode(newMode: String) {mode = newModeif (isOn) {println("❄️ 空调模式设置为 $newMode")}}fun getStatus(): String {return if (isOn) "运行中 - ${temperature}℃ $mode" else "关闭"}
}// 娱乐子系统
class EntertainmentSystem {private var tvOn = falseprivate var soundSystemOn = falseprivate var currentSource = "TV"private var volume = 50fun turnOnTV() {tvOn = trueprintln("📺 电视已开启")}fun turnOffTV() {tvOn = falseprintln("📺 电视已关闭")}fun turnOnSoundSystem() {soundSystemOn = trueprintln("🔊 音响系统已开启")}fun turnOffSoundSystem() {soundSystemOn = falseprintln("🔊 音响系统已关闭")}fun setSource(source: String) {currentSource = sourceprintln("🔊 信号源切换到 $source")}fun setVolume(level: Int) {volume = level.coerceIn(0, 100)println("🔊 音量设置为 $volume")}fun getStatus(): String {return "TV: ${if (tvOn) "开" else "关"}, 音响: ${if (soundSystemOn) "开" else "关"}"}
}// 安防子系统
class SecuritySystem {private var alarmArmed = falseprivate var doorsLocked = falseprivate var camerasOn = falsefun armAlarm() {alarmArmed = trueprintln("🚨 报警系统已布防")}fun disarmAlarm() {alarmArmed = falseprintln("🚨 报警系统已撤防")}fun lockDoors() {doorsLocked = trueprintln("🔒 所有门已上锁")}fun unlockDoors() {doorsLocked = falseprintln("🔒 所有门已解锁")}fun startSurveillance() {camerasOn = trueprintln("📹 监控系统已启动")}fun stopSurveillance() {camerasOn = falseprintln("📹 监控系统已停止")}fun getStatus(): String {return "报警: ${if (alarmArmed) "布防" else "撤防"}, 门锁: ${if (doorsLocked) "锁定" else "未锁"}, 监控: ${if (camerasOn) "开启" else "关闭"}"}
}// 窗帘子系统
class CurtainSystem {private val curtains = mutableMapOf("living_room" to 0, // 0-100 表示打开百分比"bedroom" to 0)fun open(curtain: String) {curtains[curtain] = 100println("🪟 $curtain 窗帘已完全打开")}fun close(curtain: String) {curtains[curtain] = 0println("🪟 $curtain 窗帘已完全关闭")}fun setOpenPercentage(curtain: String, percentage: Int) {curtains[curtain] = percentage.coerceIn(0, 100)println("🪟 $curtain 窗帘打开 ${percentage}%")}fun getStatus(): Map<String, Int> {return curtains.toMap()}
}

2. 创建智能家居外观类

// 智能家居外观类 - 统一入口
class SmartHomeFacade(private val lighting: LightingSystem = LightingSystem(),private val ac: AirConditioningSystem = AirConditioningSystem(),private val entertainment: EntertainmentSystem = EntertainmentSystem(),private val security: SecuritySystem = SecuritySystem(),private val curtains: CurtainSystem = CurtainSystem()
) {// 场景模式：离家模式fun leaveHome() {println("\n🏠 启动离家模式...")// 关闭所有灯光lighting.getStatus().keys.forEach { light ->if (lighting.getStatus()[light] == true) {lighting.turnOff(light)}}// 关闭空调ac.turnOff()// 关闭娱乐系统entertainment.turnOffTV()entertainment.turnOffSoundSystem()// 关闭窗帘curtains.getStatus().keys.forEach { curtain ->curtains.close(curtain)}// 启动安防系统security.lockDoors()security.armAlarm()security.startSurveillance()println("✅ 离家模式设置完成")}// 场景模式：回家模式fun arriveHome() {println("\n🏠 启动回家模式...")// 撤防安防系统security.disarmAlarm()security.unlockDoors()// 打开入口灯光lighting.turnOn("living_room")// 打开窗帘curtains.open("living_room")// 设置舒适温度ac.setTemperature(24.0)ac.turnOn()// 背景音乐entertainment.turnOnSoundSystem()entertainment.setSource("Music")entertainment.setVolume(30)println("✅ 回家模式设置完成")}// 场景模式：影院模式fun startMovieNight() {println("\n🎬 启动影院模式...")// 调暗灯光lighting.getStatus().keys.forEach { light ->lighting.dim(light, 20)}// 关闭窗帘curtains.getStatus().keys.forEach { curtain ->curtains.close(curtain)}// 开启娱乐系统entertainment.turnOnTV()entertainment.turnOnSoundSystem()entertainment.setSource("TV")entertainment.setVolume(60)// 调整空调温度ac.setTemperature(22.0)println("✅ 影院模式设置完成")}// 场景模式：睡眠模式fun startSleepMode() {println("\n😴 启动睡眠模式...")// 关闭所有灯光lighting.getStatus().keys.forEach { light ->lighting.turnOff(light)}// 关闭娱乐系统entertainment.turnOffTV()entertainment.turnOffSoundSystem()// 关闭客厅窗帘，打开卧室窗帘50%curtains.close("living_room")curtains.setOpenPercentage("bedroom", 50)// 设置睡眠温度ac.setTemperature(26.0)ac.setMode("fan")// 启动夜间安防security.armAlarm()security.startSurveillance()println("✅ 睡眠模式设置完成")}// 单独控制方法fun controlLighting(light: String, action: String, level: Int? = null) {when (action) {"on" -> lighting.turnOn(light)"off" -> lighting.turnOff(light)"dim" -> level?.let { lighting.dim(light, it) }}}fun controlTemperature(temp: Double) {ac.setTemperature(temp)if (!ac.getStatus().contains("运行中")) {ac.turnOn()}}// 获取整体状态fun getHomeStatus(): Map<String, Any> {return mapOf("lighting" to lighting.getStatus(),"ac" to ac.getStatus(),"entertainment" to entertainment.getStatus(),"security" to security.getStatus(),"curtains" to curtains.getStatus())}// 节能模式fun enableEnergySaving() {println("\n🌱 启动节能模式...")// 关闭不必要的设备lighting.getStatus().forEach { (light, isOn) ->if (isOn && light != "living_room") {lighting.turnOff(light)}}// 调整空调设置ac.setTemperature(28.0)curtains.close("living_room")println("✅ 节能模式设置完成")}
}

3. 客户端使用

// 移动APP界面
class SmartHomeApp(private val smartHome: SmartHomeFacade) {fun demonstrateScenarios() {println("=" * 50)println("🏠 智能家居控制系统演示")println("=" * 50)// 演示回家模式smartHome.arriveHome()displayStatus()Thread.sleep(2000)// 演示影院模式smartHome.startMovieNight()displayStatus()Thread.sleep(2000)// 演示睡眠模式smartHome.startSleepMode()displayStatus()Thread.sleep(2000)// 演示离家模式smartHome.leaveHome()displayStatus()Thread.sleep(2000)// 演示节能模式smartHome.enableEnergySaving()displayStatus()// 演示单独控制println("\n🎛️ 单独控制演示")smartHome.controlLighting("bedroom", "on")smartHome.controlTemperature(22.0)}fun displayStatus() {println("\n📊 当前家居状态:")val status = smartHome.getHomeStatus()status.forEach { (system, state) ->println("   $system: $state")}println()}// 语音控制接口fun voiceCommand(command: String) {when (command.toLowerCase()) {"我回家了" -> smartHome.arriveHome()"我要看电影" -> smartHome.startMovieNight()"我要睡觉了" -> smartHome.startSleepMode()"我要出门了" -> smartHome.leaveHome()"节能模式" -> smartHome.enableEnergySaving()else -> println("❌ 无法识别的指令: $command")}displayStatus()}
}// 网页控制界面
class WebControlPanel(private val smartHome: SmartHomeFacade) {fun renderDashboard() {val status = smartHome.getHomeStatus()println("""<div class="dashboard"><h1>智能家居控制面板</h1><div class="status"><h2>当前状态</h2><p>灯光: ${status["lighting"]}</p><p>空调: ${status["ac"]}</p><p>娱乐: ${status["entertainment"]}</p><p>安防: ${status["security"]}</p><p>窗帘: ${status["curtains"]}</p></div><div class="controls"><button onclick="arriveHome()">回家模式</button><button onclick="leaveHome()">离家模式</button><button onclick="movieNight()">影院模式</button><button onclick="sleepMode()">睡眠模式</button></div></div>""".trimIndent())}
}

4. 测试代码

fun main() {// 创建智能家居系统val smartHome = SmartHomeFacade()// 移动APP演示val app = SmartHomeApp(smartHome)app.demonstrateScenarios()// 语音控制测试println("\n🎤 语音控制测试:")app.voiceCommand("我回家了")app.voiceCommand("我要看电影")app.voiceCommand("节能模式")// 网页面板演示println("\n💻 网页控制面板:")val webPanel = WebControlPanel(smartHome)webPanel.renderDashboard()// 性能测试：直接操作 vs 使用外观模式println("\n⏱️ 性能对比测试:")testDirectAccess()testFacadeAccess()
}// 测试直接操作子系统的复杂性
fun testDirectAccess() {val startTime = System.currentTimeMillis()// 直接操作各个子系统实现回家模式val lighting = LightingSystem()val ac = AirConditioningSystem()val entertainment = EntertainmentSystem()val security = SecuritySystem()val curtains = CurtainSystem()// 实现回家模式需要调用多个方法security.disarmAlarm()security.unlockDoors()lighting.turnOn("living_room")curtains.open("living_room")ac.setTemperature(24.0)ac.turnOn()entertainment.turnOnSoundSystem()entertainment.setSource("Music")entertainment.setVolume(30)val duration = System.currentTimeMillis() - startTimeprintln("直接操作耗时: ${duration}ms (需要了解所有子系统细节)")
}// 测试使用外观模式的简便性
fun testFacadeAccess() {val startTime = System.currentTimeMillis()val smartHome = SmartHomeFacade()smartHome.arriveHome() // 一行代码完成复杂操作val duration = System.currentTimeMillis() - startTimeprintln("外观模式耗时: ${duration}ms (简单易用)")
}

外观模式的进阶应用

1. 分层外观模式

// 基础外观
open class BasicHomeFacade(protected val lighting: LightingSystem,protected val ac: AirConditioningSystem
) {open fun basicControl() {println("基础家居控制")}
}// 高级外观继承基础外观
class AdvancedHomeFacade(lighting: LightingSystem,ac: AirConditioningSystem,private val entertainment: EntertainmentSystem
) : BasicHomeFacade(lighting, ac) {override fun basicControl() {super.basicControl()println("增强的基础控制")}fun advancedScenarios() {startMovieNight()startPartyMode()}private fun startPartyMode() {println("🎉 启动派对模式")// 复杂的场景设置}
}

2. 动态外观模式

// 支持动态配置的外观
class DynamicFacade {private val subsystems = mutableMapOf<String, Any>()fun registerSubsystem(name: String, subsystem: Any) {subsystems[name] = subsystem}fun executeScenario(scenario: Map<String, List<String>>) {scenario.forEach { (subsystemName, actions) ->val subsystem = subsystems[subsystemName]actions.forEach { action ->executeAction(subsystem, action)}}}private fun executeAction(subsystem: Any?, action: String) {// 使用反射动态调用方法try {val method = subsystem!!::class.java.getMethod(action)method.invoke(subsystem)} catch (e: Exception) {println("无法执行操作: $action on $subsystem")}}
}

外观模式在Android开发中的应用

1. 多媒体播放器外观

class MediaPlayerFacade(private val audioManager: AudioManager,private val mediaPlayer: MediaPlayer,private val notificationManager: NotificationManager
) {fun playMedia(mediaUri: Uri, playInBackground: Boolean = false) {// 管理音频焦点audioManager.requestAudioFocus(audioFocusRequestBuilder.build())// 配置媒体播放器mediaPlayer.setDataSource(mediaUri.toString())mediaPlayer.prepareAsync()// 管理通知if (playInBackground) {showMediaNotification()}mediaPlayer.setOnPreparedListener {it.start()}}fun stopMedia() {mediaPlayer.stop()mediaPlayer.release()audioManager.abandonAudioFocus(null)hideMediaNotification()}private fun showMediaNotification() {// 创建媒体播放通知}private fun hideMediaNotification() {// 隐藏通知}
}

2. 网络请求外观

class NetworkFacade(private val okHttpClient: OkHttpClient,private val gson: Gson,private val cacheManager: CacheManager
) {suspend fun <T> request(url: String,method: String = "GET",body: Any? = null,responseType: Class<T>): Result<T> {return try {// 检查缓存val cached = cacheManager.get<T>(url)if (cached != null) {return Result.success(cached)}// 构建请求val request = buildRequest(url, method, body)// 执行网络请求val response = okHttpClient.newCall(request).execute()// 解析响应val result = parseResponse<T>(response, responseType)// 缓存结果result.onSuccess { data ->cacheManager.put(url, data)}result} catch (e: Exception) {Result.failure(e)}}private fun <T> parseResponse(response: Response, responseType: Class<T>): Result<T> {// 简化实现return try {val json = response.body?.string() ?: ""val result = gson.fromJson(json, responseType)Result.success(result)} catch (e: Exception) {Result.failure(e)}}
}