图解设计模式--Abstract Factory(抽象工厂)

将关联的零件组装成产品

Abstract Factory 模式

抽象工厂的工作是将“抽象零件”组装为“抽象产品”。

我们并不关心零件的具体实现，而是只关心接口。我们仅使用该接口将零件组装成为产品。

示例代码

文件目录

--Main.java
 |--factory
 |      |--Factory.java
 |      |--Item.java
 |      |--Link.java
 |      |--Tray.java
 |      |--Page.java
 |
 |--listfacetory
        |--ListFactory.java
        |--ListLink.java
        |--ListTray.java
        |--ListPage.java

Item.java

package abstractFactory.factory;

public abstract class Item {
    protected String caption;
    public Item(String caption) {
        this.caption = caption;
    }
    public abstract String makeHTML();
}

Link.java(AbstractProduct)

package abstractFactory.factory;

public abstract class Link extends Item {
    protected String url;
    public Link(String caption, String url) {
        super(caption);
        this.url = url;
    }
}

Tray.java(AbstractProduct)

package abstractFactory.factory;

import java.util.ArrayList;

public abstract class Tray extends Item {
    protected ArrayList tray = new ArrayList();
    public Tray(String caption) {
        super(caption);
    }
    public void add(Item item) {
        tray.add(item);
    }
}

Page.java(AbstractProduct)

package abstractFactory.factory;

import java.io.*;
import java.util.ArrayList;

public abstract class Page {
    protected String title;
    protected String author;
    protected ArrayList content = new ArrayList();

    public Page(String title, String author) {
        this.title = title;
        this.author = author;
    }

    public void add(Item item) {
        content.add(item);
    }

    public void output() {
        try {
            String filename = title + ".html";
            Writer writer = new FileWriter(filename);
            writer.write(this.makeHTML());
            writer.close();
            System.out.println(filename + "编写完成。");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public abstract String makeHTML();
}

Factory.java(AbstractFactory)

package abstractFactory.factory;

public abstract class Factory {
    public static Factory getFactory(String classname) {
        Factory factory = null;
        try {
            factory = (Factory)Class.forName(classname).newInstance();
        } catch (ClassNotFoundException e) {
            System.out.println("没有找到 " + classname + " 类。");
        } catch (Exception e) {
            e.printStackTrace();
        }
        return factory;
    }
    public abstract Link createLink(String caption, String url);
    public abstract Tray createTray(String caption);
    public abstract Page createPage(String title, String author);
}

Main.java(Client)

package abstractFactory;

import abstractFactory.factory.Factory;
import abstractFactory.factory.Link;
import abstractFactory.factory.Page;
import abstractFactory.factory.Tray;

public class Main {
    public static void main(String[] args){
        Factory factory = Factory.getFactory("abstractFactory.listfactory.ListFactory");

        Link people = factory.createLink("人民日报", "http://www.people.com.cn");
        Link gmw = factory.createLink("光明日报", "http://www.gmw.cn");

        Link us_yahoo = factory.createLink("Yahoo!", "http://www.yahoo.com");
        Link jp_yahoo = factory.createLink("Yahoo!Japan", "http://www.yahoo.co.jp");
        Link excite = factory.createLink("Excite", "http://www.excite.com");
        Link google = factory.createLink("Google", "http://www.google.com");

        Tray traynews = factory.createTray("日报");
        traynews.add(people);
        traynews.add(gmw);

        Tray trayyahoo = factory.createTray("Yahoo!");
        trayyahoo.add(us_yahoo);
        trayyahoo.add(jp_yahoo);

        Tray traysearch = factory.createTray("检索引擎");
        traysearch.add(trayyahoo);
        traysearch.add(excite);
        traysearch.add(google);

        Page page = factory.createPage("LinkPage", "杨文轩");
        page.add(traynews);
        page.add(traysearch);
        page.output();
    }
}

ListFactory.java(ConcreteFactory)

package abstractFactory.listfactory;

import abstractFactory.factory.Factory;
import abstractFactory.factory.Link;
import abstractFactory.factory.Page;
import abstractFactory.factory.Tray;

public class ListFactory extends Factory {
    public Link createLink(String caption, String url) {
        return new ListLink(caption, url);
    }

    public Tray createTray(String caption) {
        return new ListTray(caption);
    }

    public Page createPage(String title, String author) {
        return new ListPage(title, author);
    }
}

ListLink.java(ConcreteProduct)

package abstractFactory.listfactory;

import abstractFactory.factory.Link;

public class ListLink extends Link {
    public ListLink(String caption, String url) {
        super(caption, url);
    }
    public String makeHTML() {
        return "<li><a href=\"" + url +"\">" + caption + "</a></li>\n";
    }
}

ListTray.java(ConcreteProduct)

package abstractFactory.listfactory;

import abstractFactory.factory.Item;
import abstractFactory.factory.Tray;

import java.util.Iterator;

public class ListTray extends Tray {
    public ListTray(String caption) {
        super(caption);
    }

    public String makeHTML() {
        StringBuffer buffer = new StringBuffer();
        buffer.append("<li>\n");
        buffer.append(caption + "\n");
        buffer.append("<ul>\n");
        Iterator it = tray.iterator();
        while (it.hasNext()) {
            Item item = (Item)it.next();
            buffer.append(item.makeHTML());
        }
        buffer.append("</ul>\n");
        buffer.append("</li>\n");
        return buffer.toString();
    }
}

ListPage.java(ConcreteProduct)

package abstractFactory.listfactory;

import abstractFactory.factory.Item;
import abstractFactory.factory.Page;

import java.util.Iterator;

public class ListPage extends Page {
    public ListPage(String title, String author) {
        super(title, author);
    }

    public String makeHTML() {
        StringBuffer buffer = new StringBuffer();
        buffer.append("<html><head><title>" + title + "</title></head>\n");
        buffer.append("<body>\n");
        buffer.append("<h1>" + title + "</h1>\n");
        buffer.append("<ul>\n");
        Iterator it = content.iterator();
        while (it.hasNext()) {
            Item item = (Item)it.next();
            buffer.append(item.makeHTML());
        }
        buffer.append("</ul>\n");
        buffer.append("<hr><address>" + author + "</address>\n");
        buffer.append("</body></html>\n");
        return buffer.toString();
    }
}

Abstract Factory 模式中的角色

1. AbstractProduct(抽象产品)

   AbstractProduct角色负责定义AbstractFactory角色所生成的抽象零件和产品的接口。

2. AbstractFactory(抽象工厂)

   AbstractFactory角色负责定义用户生成抽象产品的接口。

3. Client(委托者)

   Client角色仅会调用 AbstractFactory 角色和 AbstractProduct 角色的接口来进行工作，对于具体的零件、产品和工厂一无所知。

4. ConcreteProduct(具体产品)

   ConcreteProduct 角色负责实现 AbstractProduct 角色的接口。

5. ConcreteFactory(具体工厂)

   ConcreteFactory 角色负责实现 AbstractFactory 角色的接口。

拓展思路

易于增加具体的工厂，难以增加新的零件。