建造者模式

Posted 2020-07-31 被罚站的树

应用场景

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将各个零件组装起来，比如我们需要组装手机，组装电脑等等。当构建的对象很复杂的时候，需要用到建造者模式。

本质

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将子组件的单独构造(由Builder来负责)和装配(由Director负责)进行了分离，这种模式适用于某个对象在构建过程复杂的情况下。由于将构建与装配解耦，不同的构建器，相同的装配也可以产生不同的对象。构建器相同,但装配不同，也可以产生不同的对象。

示例

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实体类

实体类表示各个部件具体的类，比如飞船应该有自己的实体类，然后飞船内部有轨道舱、逃逸塔、引擎的实体类。

package com.dy.xidian;

public class AirShip {
    private OrbitalModule orbitalModule;
    private Engine engine;
    private EscapeTower escapeTower;

    public OrbitalModule getOrbitalModule() {
        return orbitalModule;
    }
    public void setOrbitalModule(OrbitalModule orbitalModule) {
        this.orbitalModule = orbitalModule;
    }
    public Engine getEngine() {
        return engine;
    }
    public void setEngine(Engine engine) {
        this.engine = engine;
    }
    public EscapeTower getEscapeTower() {
        return escapeTower;
    }
    public void setEscapeTower(EscapeTower escapeTower) {
        this.escapeTower = escapeTower;
    }
}

class OrbitalModule {
    private String name;

    public OrbitalModule(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

class Engine {
    private String name;

    public Engine(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

class EscapeTower {
    private String name;

    public EscapeTower(String name) {
        super();
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

构建器接口

为了解耦，我们需要为不同构建器定义自己的接口类。

package com.dy.xidian;

public interface AirShipBuilder {
    Engine builerEngine();
    OrbitalModule builerOrbitalModule();
    EscapeTower builderEscapeTower();

}

 

构建器类

package com.dy.xidian;

public class AirShipBuilderImpl implements AirShipBuilder {

    @Override
    public Engine builerEngine() {
        System.out.println("发动机");
        return new Engine("构建发动机");
    }

    @Override
    public OrbitalModule builerOrbitalModule() {
        System.out.println("轨道舱");
        return new OrbitalModule("构建轨道舱");
    }

    @Override
    public EscapeTower builderEscapeTower() {
        System.out.println("逃逸塔");
        return new EscapeTower("构建逃逸塔");
    }

}

 

装配器接口 

装配器通过装配应该返回一个装配好的对象

package com.dy.xidian;

public interface AirShipDirector {
    AirShip directorAirShip();
}

 

装配器类

package com.dy.xidian;

public class AirShipDirectorImpl implements AirShipDirector {
    private AirShipBuilder builder;
    public AirShipDirectorImpl(AirShipBuilder builder) {
        this.builder = builder;
    }

    @Override
    public AirShip directorAirShip() {
        Engine e = builder.builerEngine();
        OrbitalModule o = builder.builerOrbitalModule();
        EscapeTower et = builder.builderEscapeTower();

        AirShip ship = new AirShip();
        ship.setEngine(e);
        ship.setEscapeTower(et);
        ship.setOrbitalModule(o);
        return ship;
    }

}

 

装配器在装配时首先要通过builder类将各个部件构造出来,然后对其组装。这里的builder可以使用简单工厂模式来生成各个部件。

客户

package com.dy.xidian;

public class Clinet {

    public static void main(String[] args) {
        AirShipDirector director = new AirShipDirectorImpl(
                new AirShipBuilderImpl());
        AirShip ship = director.directorAirShip();
    }

}

 

客户选择一个具体的构建器,让装配器对其进行组装。

应用

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StringBuilder类的append方法

JDOM中的DOMBuiler，SAXBuilder方法