Proxy

最新推荐文章于 2024-11-19 01:15:00 发布

aimyxmu

最新推荐文章于 2024-11-19 01:15:00 发布

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分类专栏： Design Pattern 文章标签： image string initialization class object interface

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Provide a placeholder or proxy for another project to access it.

Here are several situations in which the proxy pattern is applicable.

一、A virtual proxy which creates an expensive object on demand.Defer the full cost of an huge object's creation and initialization until we actually need it.We can cache additional information about the real subject so that we can postpone accessing it.

The ImageProxy below is a example of such a proxy.

An document contains expensive images.But opening the document should be fast.So we need avoid creating all expensive objects at once when the document is opened.

Solution: Create expensive objects on demand.When the image is invisible, the description of the image should show in the place of the image.

Interface:Image

package com.aimy.design.examples.proxy; public interface Image { public abstract void draw(); public abstract void handleMouse(); public abstract String getDesc(); }

Subject:

package com.aimy.design.examples.proxy; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; public class ImageImpl implements Image { private String filename; private InputStream is; private String desc; public ImageImpl(String filename){ this.filename = filename; } public void draw() { // TODO Auto-generated method stub System.out.println("Drawing the expensive Image"); FileOutputStream os; try { is = new FileInputStream(filename); int i = filename.indexOf(".gif"); os = new FileOutputStream(filename.substring(0, i)+"Copy"+".gif"); int c; while((c=is.read())!=-1){ os.write(c); } is.close(); os.close(); System.out.println("Copying the expensive Image is done"); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public void handleMouse() { // TODO Auto-generated method stub System.out.println("Controlling the expensive Image by mouse"); } public String getDesc(){ return this.desc; } }

subjectProxy:

package com.aimy.design.examples.proxy; public class ImageImplProxy implements Image { private Image image; private String desc; private String fileName; public ImageImplProxy(String fileName,String desc){ this.fileName = fileName; this.desc = desc; } public void draw() { // TODO Auto-generated method stub this.getImage().draw(); } public void handleMouse() { // TODO Auto-generated method stub this.getImage().handleMouse(); } public Image getImage(){ if(image ==null) image = new ImageImpl(fileName); return image; } public String getDesc(){ System.out.println("Get image description form database"); System.out.println("Display image description on the place of the image"); return fileName; } }

Main:document

package com.aimy.design.examples.proxy; public class Document { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub Image image = new ImageImplProxy("./com/aimy/design/examples/proxy/clip.gif","Flow"); //Use the description to replace the image while opening the document image.getDesc(); //Draw the image on demand image.draw(); image.handleMouse(); } }