代理模式

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代理模式(proxy)，为其他对象提供一种代理以控制对这个对象的访问。

Class Diagram

Implementation

代理接口

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public interface Image {
    void showImage();
}

被代理类

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public class HighResolutionImage implements Image {
    private URL imageURL;
    private long startTime;
    private int height;
    private int width;

    public int getHeight() {
        return height;
    }

    public int getWidth() {
        return width;
    }

    public HighResolutionImage(URL imageURL) {
        this.imageURL = imageURL;
        this.startTime = System.currentTimeMillis();
        this.width = 600;
        this.height = 600;
    }

    public boolean isLoad() {
        // 模拟图片加载，延迟 3s 加载完成
        long endTime = System.currentTimeMillis();
        return endTime - startTime > 3000;
    }

    @Override
    public void showImage() {
        System.out.println("Real Image: " + imageURL);
    }
}

代理类

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public class ImageProxy implements Image {

    private HighResolutionImage highResolutionImage;

    public ImageProxy(HighResolutionImage highResolutionImage) {
        this.highResolutionImage = highResolutionImage;
    }

    @Override
    public void showImage() {
        while (!highResolutionImage.isLoad()) {
            try {
                System.out.println("Temp Image: " + highResolutionImage.getWidth() + " " + highResolutionImage.getHeight());
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        highResolutionImage.showImage();
    }
}

测试类

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public class ProxyTest {

    @Test
    public void test() throws Exception{
        String image = "http://image.jpg";
        URL url = new URL(image);
        HighResolutionImage highResolutionImage = new HighResolutionImage(url);
        ImageProxy imageProxy = new ImageProxy(highResolutionImage);
        imageProxy.showImage();
    }
}

Example

  • java.lang.reflect.Proxy
  • RMI

Reflence