建造者模式(Builder)

建造者模式是对象创建型设计模式之一,他主要用于构造复杂对象,而这个复杂对象则可以由多组不同的产品族构成,其结构原理图如下:

其中关键部件有两个

1. Builder

Builder定义了生产复杂对象的组件的抽象接口(BuildPart)和获取这个复杂对象的方法(GetResult),但他自己本身并不装配对象,简言之Builder是生成复杂对象部件的接口提供者

2. Director

Director定义了装配复杂对象的接口,它使用Builder提供的生产复杂对象组件的方法来生成组件,并将其装配起来,最后调用GetResult返回该复杂对象

例子:

Component

Body组件族

public abstract class Body {
    public abstract void showBody();
}


public class LongBody extends Body {

    @Override
    public void showBody() {
        System.out.println("I have a long body");
    }
}


public class ShortBody extends Body {

    @Override
    public void showBody() {
        System.out.println("I hava a short body");
    }
}

Head组件族

public abstract class Head {
    public abstract void showHead();
}


public class BigHead extends Head {

    @Override
    public void showHead() {
        System.out.println("I have a very very big head!");
    }
}


public class SmallHead extends Head {

    @Override
    public void showHead() {
        System.out.println("I only have a really small head!");
    }
}

复杂对象Man

public class Man {
    private Head head;
    private Body body;

    public void setHead(Head head) {
        this.head = head;
    }

    public void setBody(Body body) {
        this.body = body;
    }

    public void showMe() {
        head.showHead();
        body.showBody();
    }
}

Builder

public abstract class ManBuilder {

    protected Man man;

    public Man getMan() {
        return man;
    }

    public void buildMan() {
        man = new Man();
    }

    public abstract void buildHead();

    public abstract void buildBody();
}


public class BigManBuilder extends ManBuilder {

    @Override
    public void buildHead() {
        man.setHead(new BigHead());
    }

    @Override
    public void buildBody() {
        man.setBody(new LongBody());
    }
}


public class SmallManBuilder extends ManBuilder {

    @Override
    public void buildHead() {
        man.setHead(new SmallHead());
    }

    @Override
    public void buildBody() {
        man.setBody(new ShortBody());
    }
}


public class AbnormalManBuilder extends ManBuilder {

    @Override
    public void buildHead() {
        man.setHead(new BigHead());
    }

    @Override
    public void buildBody() {
        man.setBody(new ShortBody());
    }
}

Director

public class ManDirector {

    public Man createMan(ManBuilder builder) {
        builder.buildMan();
        builder.buildHead();
        builder.buildBody();
        return builder.getMan();
    }
}

客户端

public class Client {

    public static void main(String[] args) {
        ManBuilder bigManBuilder = new BigManBuilder();
        ManBuilder smallManBuilder = new SmallManBuilder();
        ManBuilder abnormalManBuilder = new AbnormalManBuilder();

        ManDirector manDirector = new ManDirector();

        Man bigMan = manDirector.createMan(bigManBuilder);
        Man smallMan = manDirector.createMan(smallManBuilder);
        Man abnormalMan = manDirector.createMan(abnormalManBuilder);

        bigMan.showMe();
        smallMan.showMe();
        abnormalMan.showMe();
    }
}

优势:

1. 隐藏产品的内部结构(Builder)和其装配过程(Director),在改变产品的内部表示时只需要创建新的Builder(例如使用不同的Head和Body构造Man)

2. 解耦复杂对象的构建过程(Director)和表示方式(Builder),使得可以生成不同的构造过程(Director),并在不同的Director复用相同的Builder

3. 对构建过程进行精细控制,可以在Director内对构建构成进行控制

4. 定义Director 固定产品的构造过程,使产品的构造不会出错(例如漏掉某些构造部件的过程)