13) Proxy Pattern

类别：

 Structural Pattern

问题：

操纵一个对象时碍手碍脚，与装饰者模式不同之处：

装饰者是接口方法，授权小

代理则是整个类，授权大

方案：

 

 

 

示例：

 

public class ProxyPatternDemo {
    
    public static void main(final String[] arguments) {
        final Image image1 = new ProxyImage("HiRes_10MB_Photo1");
        final Image image2 = new ProxyImage("HiRes_10MB_Photo2");

        image1.displayImage(); // loading necessary
        image1.displayImage(); // loading unnecessary
        image2.displayImage(); // loading necessary
        image2.displayImage(); // loading unnecessary
        image1.displayImage(); // loading unnecessary
    }
}

interface Image {
    public void displayImage();
}

// On System A
class RealImage implements Image {

    private String filename = null;

    /**
     * Constructor
     * 
     * @param filename
     */
    public RealImage(final String filename) {
        this.filename = filename;
        loadImageFromDisk();
    }

    /**
     * Loads the image from the disk
     */
    private void loadImageFromDisk() {
        System.out.println("Loading   " + filename);
    }

    /**
     * Displays the image
     */
    public void displayImage() {
        System.out.println("Displaying " + filename);
    }

}

// On System B
class ProxyImage implements Image {

    private RealImage image = null;
    private String filename = null;

    /**
     * Constructor
     * 
     * @param filename
     */
    public ProxyImage(final String filename) {
        this.filename = filename;
    }

    /**
     * Displays the image
     */
    public void displayImage() {
        if (image == null) {
            image = new RealImage(filename);
        }
        image.displayImage();
    }

}

 

应用：

 

不足：(

 

优化：）