Java设计模式-外观模式

目录

一、影院管理项目

二、外观模式

（一）基本介绍

（二）原理类图

（三）解决影院管理

（四）注意事项和细节

（五）外观模式在MyBatis框架应用的源码分析

---

一、影院管理项目

传统方式解决影院管理就是直接用一个类来操作各个设备，类似代码如下：

ClientTest {
    public static void main() {
        //1. 创建相关的对象
        //2. 调用创建的各个对象的一系列方法
        // 3. 调用DVDPlayer 对象的play方法
    }
}

?分析：

二、外观模式

（一）基本介绍

（二）原理类图

外观模式可以理解为转换一群接口，客户只要调用一个接口，而不用调用多个接口才能达到目的。比如：在pc 上安装软件的时候经常有一键安装选项（省去选择安装目录、安装的组件等等），还有就是手机的重启功能 （把关机和启动合为一个操作）。

外观模式就是解决多个复杂接口带来的使用 困难，起到简化用户操作的作用

（三）解决影院管理

类图如下：

各种设备

public class DVDPlayer {
	
	//使用单例模式, 使用饿汉式
	private static DVDPlayer instance = new DVDPlayer();
	
	public static DVDPlayer getInstanc() {
		return instance;
	}
	
	public void on() {
		System.out.println(" dvd on ");
	}
	public void off() {
		System.out.println(" dvd off ");
	}
	
	public void play() {
		System.out.println(" dvd is playing ");
	}

	public void pause() {
		System.out.println(" dvd pause ..");
	}
}

===========================================================
// 爆米花机
public class Popcorn {
	
	private static Popcorn instance = new Popcorn();
	
	public static Popcorn getInstance() {
		return instance;
	}
	
	public void on() {
		System.out.println(" popcorn on ");
	}
	
	public void off() {
		System.out.println(" popcorn off ");
	}
	
	public void pop() {
		System.out.println(" popcorn is poping  ");
	}
}

===========================================================
public class Projector {

	private static Projector instance = new Projector();
	
	public static Projector getInstance() {
		return instance;
	}
	
	public void on() {
		System.out.println(" Projector on ");
	}
	
	public void off() {
		System.out.println(" Projector ff ");
	}
	
	public void focus() {
		System.out.println(" Projector is Projector  ");
	}
	
	//...
}

===========================================================
public class Screen {

	private static Screen instance = new Screen();
	
	public static Screen getInstance() {
		return instance;
	}
	
	
	
	
	public void up() {
		System.out.println(" Screen up ");
	}
	
	public void down() {
		System.out.println(" Screen down ");
	}
	

}

===========================================================
public class Stereo {

	private static Stereo instance = new Stereo();
	
	public static Stereo getInstance() {
		return instance;
	}
	
	public void on() {
		System.out.println(" Stereo on ");
	}
	
	public void off() {
		System.out.println(" Screen off ");
	}
	
	public void up() {
		System.out.println(" Screen up.. ");
	}
	
	//...
}

===========================================================
public class TheaterLight {

	private static TheaterLight instance = new TheaterLight();

	public static TheaterLight getInstance() {
		return instance;
	}

	public void on() {
		System.out.println(" TheaterLight on ");
	}

	public void off() {
		System.out.println(" TheaterLight off ");
	}

	public void dim() {
		System.out.println(" TheaterLight dim.. ");
	}

	public void bright() {
		System.out.println(" TheaterLight bright.. ");
	}
}

外观类HomeTheaterFacade?

public class HomeTheaterFacade {
	
	//定义各个子系统对象
	private TheaterLight theaterLight;
	private Popcorn popcorn;
	private Stereo stereo;
	private Projector projector;
	private Screen screen;
	private DVDPlayer dVDPlayer;
	
	
	//构造器
	public HomeTheaterFacade() {
		super();
		this.theaterLight = TheaterLight.getInstance();
		this.popcorn = Popcorn.getInstance();
		this.stereo = Stereo.getInstance();
		this.projector = Projector.getInstance();
		this.screen = Screen.getInstance();
		this.dVDPlayer = DVDPlayer.getInstanc();
	}

	//操作分成 4 步
	
	public void ready() {
		popcorn.on();
		popcorn.pop();
		screen.down();
		projector.on();
		stereo.on();
		dVDPlayer.on();
		theaterLight.dim();
	}
	
	public void play() {
		dVDPlayer.play();
	}
	
	public void pause() {
		dVDPlayer.pause();
	}
	
	public void end() {
		popcorn.off();
		theaterLight.bright();
		screen.up();
		projector.off();
		stereo.off();
		dVDPlayer.off();
	}
}

客户端调用

public class Client {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		//这里直接调用各个设备会很麻烦

		// 创建HomeTheaterFacade类，隐藏内部细节
		HomeTheaterFacade homeTheaterFacade = new HomeTheaterFacade();
		homeTheaterFacade.ready();
		homeTheaterFacade.play();
		
		
		homeTheaterFacade.end();
	}

}

（四）注意事项和细节

（五）外观模式在MyBatis框架应用的源码分析

MyBatis 中的Configuration 去创建MetaObject 对象使用到外观模式

configuration相当于外观类，里面聚合了下面三个类，然后在构造器中为其赋值

在newMeta方法中调用了MetaObject.forObject方法

大致的类图如下：?