享元模式（Flyweight）

享元模式（Flyweight），运用共享技术有效地支持大量细粒度的对象。
PS:比如String的对象，利用享元模式概念，两个栈指针指向同一个堆地址。
享元模式可以避免大量非常相似类的开销。在程序设计中，有时需要生产大量细粒度的类实例来表示数据。如果能发现这些实例除了几个参数之外基本都是相同的，有时就能受大幅度地减少需要实例化的类的数量。如果能把那些参数移到类实例的外面，在方法调用时将它们传递进来，就可以通过共享大幅度地减少单实例的数目。

主方法

public class main {
    public static void main(String[] args) {
        WebSiteFactory webSiteFactory = new WebSiteFactory();

        WebSite fx = webSiteFactory.getWebSiteCategory("产品展示");
        fx.use(new User("小菜"));

        WebSite fy = webSiteFactory.getWebSiteCategory("产品展示");
        fy.use(new User("大鸟"));

        WebSite fz = webSiteFactory.getWebSiteCategory("产品展示");
        fz.use(new User("娇娇"));

        WebSite fl = webSiteFactory.getWebSiteCategory("博客");
        fl.use(new User("老顽童"));

        WebSite fm = webSiteFactory.getWebSiteCategory("博客");
        fm.use(new User("桃谷六仙"));

        WebSite fn = webSiteFactory.getWebSiteCategory("博客");
        fn.use(new User("南海鳄神"));

        System.out.println(String.format("得到网站分类总数为：{%d}", webSiteFactory.countWebSite()));
    }
}

用户类

public class User {
    public User(String name) {
        this.name = name;
    }

    private String name;

    public String getName() {
        return name;
    }

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

享元抽象类

/**
 * 网站抽象类
 */
public abstract class WebSite {
    public abstract void use(User user);
}

享元实现类

/**
 * 具体网站类
 */
public class WebSiteImpl extends WebSite {
    private String name = "";

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

    public void use(User user) {
        System.out.println("网站分类：" + name + " 用户：" + user.getName());
    }
}

享元工厂类

import java.util.concurrent.ConcurrentHashMap;
public class WebSiteFactory {
    private ConcurrentHashMap<String, WebSiteImpl> flyweights = new ConcurrentHashMap<String, WebSiteImpl>();

    public WebSite getWebSiteCategory(String key) {
        if (!flyweights.contains(key)) {
            flyweights.put(key, new WebSiteImpl(key));
        }
        return flyweights.get(key);
    }

    public int countWebSite() {
        return flyweights.size();
    }
}