【图解设计模式】Abstract Factory模式

抽象工厂将抽象零件组装为抽象产品。

示例

将带有层次关系的链接的集合制作成HTML文件。

类图

Item类

package factory;

public abstract class Item {
    protected String caption;

    public Item(String caption) {
        this.caption = caption;
    }

    public abstract String makeHTML();
}

Link类

package factory;

public abstract class Link extends Item {
    protected String url;

    public Link(String caption, String url) {
        super(caption);
        this.url = url;
    }
}

Tray类

package 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类

package factory;

import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
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类

package 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.err.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类

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

public class Main {

    public static void main(String[] args) {
        if (args.length != 1) {
            System.out.println("Usage: java Main class.name.of.ConcreteFactory");
            System.out.println("Example 1: java Main listfactory.ListFactory");
            System.out.println("Example 2: java Main tablefactory.TableFactory");
            System.exit(0);
        }

        Factory factory = Factory.getFactory(args[0]);

        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类

package listfactory;

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

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

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

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

ListLink类

package listfactory;

import factory.Link;

public class ListLink extends Link {
    public ListLink(String caption, String url) {
        super(caption, url);
    }

    @Override
    public String makeHTML() {
        return "    <li><a href=\"" + url + "\">" + caption + "</a></li>\n";
    }
}

ListTray类

package listfactory;

import factory.Item;
import factory.Tray;

import java.util.Iterator;

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

    @Override
    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类

package listfactory;

import factory.Item;
import factory.Page;

import java.util.Iterator;

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

    @Override
    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>");
        buffer.append("</body></html>\n");
        return buffer.toString();
    }
}

运行结果

<html><head><title>LinkPage</title></head>
<body>
<h1>LinkPage</h1>
<ul>
<li>
日报
<ul>
    <li><a href="http://www.people.com.cn/">人民日报</a></li>
    <li><a href="http://www.gmw.cn/">光明日报</a></li>
</ul>
</li>
<li>
检索引擎
<ul>
<li>
Yahoo!
<ul>
    <li><a href="http://www.yahoo.com/">Yahoo!</a></li>
    <li><a href="http://www.yahoo.co.jp/">Yahoo!Japan</a></li>
</ul>
</li>
    <li><a href="http://www.excite.com/">Excite</a></li>
    <li><a href="http://www.google.com/">Google</a></li>
</ul>
</li>
</ul>
<hr><address>杨文轩</address></body></html>

TableFactory类

package tablefactory;

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

public class TableFactory extends Factory {
    @Override
    public Link createLink(String caption, String url) {
        return new TableLink(caption, url);
    }

    @Override
    public Tray createTray(String caption) {
        return new TableTray(caption);
    }

    @Override
    public Page createPage(String title, String author) {
        return new TablePage(title, author);
    }
}

TableLink类

package tablefactory;

import factory.Link;

public class TableLink extends Link {
    public TableLink(String caption, String url) {
        super(caption, url);
    }

    @Override
    public String makeHTML() {
        return "<td><a href=\"" + url + "\">" + caption + "</a></td>\n";
    }
}

TableTray类

package tablefactory;

import factory.Item;
import factory.Tray;

import java.util.Iterator;

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

    @Override
    public String makeHTML() {
        StringBuffer buffer = new StringBuffer();
        buffer.append("<td>");
        buffer.append("<table width=\"100%\" border=\"1\"><tr>");
        buffer.append("<td bgcolor=\"#cccccc\" align=\"center\" colspan=\""
                        + tray.size() + "\"><b>" + caption + "</b></td>");
        buffer.append("</tr>\n");
        buffer.append("<tr>\n");

        Iterator it = tray.iterator();
        while (it.hasNext()) {
            Item item = (Item) it.next();
            buffer.append(item.makeHTML());
        }

        buffer.append("</tr></table>");
        buffer.append("</td>");
        return buffer.toString();
    }
}

TablePage类

package tablefactory;

import factory.Item;
import factory.Page;

import java.util.Iterator;

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

    @Override
    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("<table width=\"80%\" border=\"3\">\n");

        Iterator it = content.iterator();
        while (it.hasNext()) {
            Item item = (Item) it.next();
            buffer.append("<tr>" + item.makeHTML() + "</tr>");
        }

        buffer.append("</table>\n");
        buffer.append("<hr><address>" + author + "</address>");
        buffer.append("</body></html>\n");
        return buffer.toString();
    }
}

运行结果

<html><head><title>LinkPage</title></head>
<body>
<h1>LinkPage</h1>
<table width="80%" border="3">
<tr><td><table width="100%" border="1"><tr><td bgcolor="#cccccc" align="center" colspan="2"><b>日报</b></td></tr>
<tr>
<td><a href="http://www.people.com.cn/">人民日报</a></td>
<td><a href="http://www.gmw.cn/">光明日报</a></td>
</tr></table></td></tr><tr><td><table width="100%" border="1"><tr><td bgcolor="#cccccc" align="center" colspan="3"><b>检索引擎</b></td></tr>
<tr>
<td><table width="100%" border="1"><tr><td bgcolor="#cccccc" align="center" colspan="2"><b>Yahoo!</b></td></tr>
<tr>
<td><a href="http://www.yahoo.com/">Yahoo!</a></td>
<td><a href="http://www.yahoo.co.jp/">Yahoo!Japan</a></td>
</tr></table></td><td><a href="http://www.excite.com/">Excite</a></td>
<td><a href="http://www.google.com/">Google</a></td>
</tr></table></td></tr></table>
<hr><address>杨文轩</address></body></html>

登场角色

AbstractProduct（抽象产品）

AbstractProduct角色负责定义AbstractFactory角色所产生的抽象零件和产品的接口（API）。在示例程序中，由Link类、Tray类和Page类扮演此角色。

AbstractFactory（抽象工厂）

AbstractFactory角色负责定义用于生成抽象产品的接口（API）。在示例程序中，由Factory类扮演此角色。

Client（委托者）

Client角色仅会调用AbstractFactory角色和AbstractProduct角色的接口（API）来进行工作，对于具体的零件、产品和工厂一无所知。在示例程序中，由Main类扮演此角色。

ConcreteProduct（具体产品）

ConcreteProduct角色负责实现AbstractProduct角色的接口（API）。在示例程序中，由以下包中的以下类扮演此角色：

• listfactory包：ListLink类、ListTray类和ListPage类
• tablefactory包：TableLink类、TableTray类和TablePage类

ConcreteFactory（具体工厂）

ConcreteFactory角色负责实现AbstractFactory角色的接口（API）。在示例程序中，由以下包中的以下类扮演此角色：

• listfactory包：ListFactory类
• tablefactory包：TableFactory类

类图