Java描述设计模式(12)：外观模式

本文源码：GitHub·点这里 || GitEE·点这里

一、生活场景

1、场景描述

2、代码图解

3、代码实现

/**
 * 外观模式描述饭店就餐流程
 */
public class C01_InScene {
    public static void main(String[] args) {
        EatAppFacade eatAppFacade = new EatAppFacade () ;
        eatAppFacade.dining();
    }
}
// 预定
class Booking {
    private static Booking booking = new Booking() ;
    public static Booking getInstance (){
        return booking ;
    }
    public void bookPlace (){
        System.out.println("位置预定...");
    }
}
// 点餐
class TakeOrder {
    private static TakeOrder takeOrder = new TakeOrder ();
    public static TakeOrder getInstance (){
        return takeOrder ;
    }
    public void orderDishes (){
        System.out.println("点餐...");
    }
}
// 付款
class Payment {
    private static Payment payment = new Payment () ;
    public static Payment getInstance (){
        return payment ;
    }
    public void payMoney (){
        System.out.println("结账...");
    }
}
// 点餐APP
class EatAppFacade {
    private Booking booking ;
    private TakeOrder takeOrder ;
    private Payment payment ;
    public EatAppFacade (){
        this.booking = Booking.getInstance() ;
        this.takeOrder = TakeOrder.getInstance() ;
        this.payment = Payment.getInstance() ;
    }
    // 就餐流程
    public void dining (){
        booking.bookPlace();
        takeOrder.orderDishes();
        payment.payMoney();
    }
}

二、外观设计模式

1、基本简介

2、模式图解

3、核心角色

• 外观角色

• 子模块角色

• 客户端角色

4、源代码实现

public class C02_Facade {
    public static void main(String[] args) {
        Facade facade = new Facade();
        facade.clientNeed1();
        facade.clientNeed2();
    }
}
class ModuleA {
    public void testA (){
        System.out.println("ModuleA.testA()");
    }
}
class ModuleB {
    public void testB (){
        System.out.println("ModuleB.testB()");
    }
}
class ModuleC {
    public void testC (){
        System.out.println("ModuleC.testC()");
    }
}
class Facade {
    /**
     * 客户需求1
     */
    public void clientNeed1 (){
        ModuleA moduleA = new ModuleA();
        moduleA.testA();
        ModuleB moduleB = new ModuleB();
        moduleB.testB();
    }
    /**
     * 客户需求1
     */
    public void clientNeed2 (){
        ModuleB moduleB = new ModuleB();
        moduleB.testB();
        ModuleC moduleC = new ModuleC();
        moduleC.testC();
    }
}

三、Mybatis应用场景

1、使用场景

• org.apache.ibatis.session.Configuration
• org.apache.ibatis.reflection.MetaObject

Configuration 创建 MetaObject 的时候。

2、Configuration源码

public class Configuration {
    protected ObjectFactory objectFactory;
    protected ObjectWrapperFactory objectWrapperFactory;
    public Configuration() {
        this.objectFactory = new DefaultObjectFactory();
        this.objectWrapperFactory = new DefaultObjectWrapperFactory();
    }
    public MetaObject newMetaObject(Object object) {
        return MetaObject.forObject(object, this.objectFactory, this.objectWrapperFactory);
    }
    // ... 省去其他源码
}

3、MetaObject 源码

public static MetaObject forObject(Object object,
                                   ObjectFactory objectFactory,
                                   ObjectWrapperFactory objectWrapperFactory) {
    return object == null ?
            SystemMetaObject.NULL_META_OBJECT :
            new MetaObject(object, objectFactory, objectWrapperFactory);
}

四、优缺点总结

五、源代码地址

GitHub·地址
https://github.com/cicadasmile/model-arithmetic-parent
GitEE·地址
https://gitee.com/cicadasmile/model-arithmetic-parent