吴裕雄--天生自然轻量级JAVA EE企业应用开发Struts2Sping4Hibernate整合开发学习笔记：企业应用开发的思考和策略_Proxy

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2016, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */

// 使用该BigImage模拟一个很大图片
public class BigImage implements Image
{
    public BigImage()
    {
        try
        {
            // 程序暂停3s模式模拟系统开销
            Thread.sleep(3000);
            System.out.println("图片装载成功...");
        }
        catch (InterruptedException ex)
        {
            ex.printStackTrace();
        }
    }
    // 实现Image里的show()方法
    public void show()
    {
        System.out.println("绘制实际的大图片");
    }
}

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2016, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public class BigImageTest
{
    public static void main(String[] args)
    {
        long start = System.currentTimeMillis();
        // 程序返回一个Image对象，该对象只是BigImage的代理对象
        Image image = new ImageProxy(null);
        System.out.println("系统得到Image对象的时间开销:" +
             (System.currentTimeMillis() - start));
        // 只有当实际调用image代理的show()方法时，程序才会真正创建被代理对象。
        image.show();
    }
}

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2016, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public interface Image
{
    void show();
}

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2016, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public class ImageProxy implements Image
{
    // 组合一个image实例，作为被代理的对象
    private Image image;
    // 使用抽象实体来初始化代理对象
    public ImageProxy(Image image)
    {
        this.image = image;
    }
    /**
     * 重写Image接口的show()方法
     * 该方法用于控制对被代理对象的访问，
     * 并根据需要负责创建和删除被代理对象
     */
    public void show()
    {
        // 只有当真正需要调用image的show方法时才创建被代理对象
        if (image == null)
        {
            image = new BigImage();
        }
        image.show();
    }
}