CamelAct

Overview

프록시 패턴은 컴퓨터 프로그래밍의 소프트웨어 디자인 패턴 중 하나입니다.

일반적으로 프록시는 다른 것에 대한 인터페이스 역할을 하는 클래스입니다. 프록시는 모든 것에 대한 인터페이스 역할을 할 수 있습니다(예: 네트워크 연결, 메모리의 큰 개체, 파일 또는 복제할 수 없거나 수요가 많은 리소스).

프록시 패턴의 잘 알려진 예는 참조 카운트 스마트 포인터 개체입니다.

복잡한 객체의 복사본이 여러 개 존재해야 하는 상황에서 프록시 패턴을 플라이웨이트 패턴과 결합하여 애플리케이션의 메모리 사용량을 줄일 수 있습니다.

장점
전처리 및 후처리에 사용하기 쉽습니다. (B가 C에게 묻기 전에 다른 작업을 전처리할 수 있음)
특정 방법에 대한 보안은 양호합니다. (B가 C에게 요청한다는 사실은 A가 무슨 일이 일어나고 있는지 정확히 알기 어렵게 만든다)

불리
절차적 패턴을 사용하면 가독성이 떨어집니다. (A->B-C의 구조는 누군가 거쳐야 하는 구조입니다. 이런 경우가 많으면 가독성이 떨어질 수 있습니다.)

Structure

Code Example

package com.example.design.pattern;

import java.awt.Component;
import java.awt.Graphics;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Enumeration;
import java.util.Hashtable;

import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;

class ImageComponent extends JComponent {
	private static final long serialVersionUID = 1L;
	private Icon icon;

	public ImageComponent(Icon icon) {
		this.icon = icon;
	}

	public void setIcon(Icon icon) {
		this.icon = icon;
	}

	public void paintComponent(Graphics g) {
		super.paintComponent(g);
		int w = icon.getIconWidth();
		int h = icon.getIconHeight();
		int x = (800 - w)/2;
		int y = (600 - h)/2;
		icon.paintIcon(this, g, x, y);
	}
}

class ImageProxy implements Icon {
	volatile ImageIcon imageIcon;
	final URL imageURL;
	Thread retrievalThread;
	boolean retrieving = false;

	public ImageProxy(URL url) {
		imageURL = url;
	}

	@Override
	public int getIconWidth() {
		if (imageIcon != null) {
			return imageIcon.getIconWidth();
		} else {
			return 800;
		}
	}

	@Override
	public int getIconHeight() {
		if (imageIcon != null) {
			return imageIcon.getIconHeight();
		} else {
			return 600;
		}
	}

	synchronized void setImageIcon(ImageIcon imageIcon) {
		this.imageIcon = imageIcon;
	}

	@Override
	public void paintIcon(final Component c, Graphics g, int x, int y) {
		if (imageIcon != null) {
			imageIcon.paintIcon(c, g, x, y);
		} else {
			g.drawString("Loading CD cover, please wait...", x + 300, y + 190);
			if (!retrieving) {
				retrieving = true;

				retrievalThread = new Thread(new Runnable() {
					public void run() {
						try {
							setImageIcon(new ImageIcon(imageURL, "CD Cover"));
							c.repaint();
						} catch (Exception e) {
							e.printStackTrace();
						}
					}
				});
				retrievalThread.start();
			}
		}
	}
}

public class MyProxy {

	ImageComponent imageComponent;
	JFrame frame = new JFrame("CD Cover Viewer");
	JMenuBar menuBar;
	JMenu menu;
	Hashtable<String, String> cds = new Hashtable<String, String>();

	public static void main(String[] args) throws Exception {
		new MyProxy();
	}

	public MyProxy() throws Exception{
		cds.put("Buddha Bar","http://images.amazon.com/images/P/B00009XBYK.01.LZZZZZZZ.jpg");
		cds.put("Ima","http://images.amazon.com/images/P/B000005IRM.01.LZZZZZZZ.jpg");
		cds.put("Karma","http://images.amazon.com/images/P/B000005DCB.01.LZZZZZZZ.gif");
		cds.put("MCMXC A.D.","http://images.amazon.com/images/P/B000002URV.01.LZZZZZZZ.jpg");
		cds.put("Northern Exposure","http://images.amazon.com/images/P/B000003SFN.01.LZZZZZZZ.jpg");
		cds.put("Selected Ambient Works, Vol. 2","http://images.amazon.com/images/P/B000002MNZ.01.LZZZZZZZ.jpg");

		URL initialURL = new URL((String)cds.get("Selected Ambient Works, Vol. 2"));
		menuBar = new JMenuBar();
		menu = new JMenu("Favorite CDs");
		menuBar.add(menu);
		frame.setJMenuBar(menuBar);

		for (Enumeration<String> e = cds.keys(); e.hasMoreElements();) {
			String name = (String)e.nextElement();
			JMenuItem menuItem = new JMenuItem(name);
			menu.add(menuItem); 
			menuItem.addActionListener(event -> {
				imageComponent.setIcon(new ImageProxy(getCDUrl(event.getActionCommand())));
				frame.repaint();
			});
		}

		// set up frame and menus

		Icon icon = new ImageProxy(initialURL);
		imageComponent = new ImageComponent(icon);
		frame.getContentPane().add(imageComponent);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setSize(800,600);
		frame.setVisible(true);

	}

	URL getCDUrl(String name) {
		try {
			return new URL((String) cds.get(name));
		} catch (MalformedURLException e) {
			e.printStackTrace();
			return null;
		}
	}

}

Console Result

Additional Code Example

package com.example.design.pattern.core;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.HashMap;

class NonOwnerInvocationHandler implements InvocationHandler {
	PersonBean person;

	public NonOwnerInvocationHandler(PersonBean person) {
		this.person = person;
	}

	public Object invoke(Object proxy, Method method, Object[] args) throws IllegalAccessException {

		try {
			if (method.getName().startsWith("get")) {
				return method.invoke(person, args);
			} else if (method.getName().equals("setHotOrNotRating")) {
				return method.invoke(person, args);
			} else if (method.getName().startsWith("set")) {
				throw new IllegalAccessException();
			}
		} catch (InvocationTargetException e) {
			e.printStackTrace();
		}
		return null;
	}
}

class OwnerInvocationHandler implements InvocationHandler {
	PersonBean person;

	public OwnerInvocationHandler(PersonBean person) {
		this.person = person;
	}

	public Object invoke(Object proxy, Method method, Object[] args) throws IllegalAccessException {

		try {
			if (method.getName().startsWith("get")) {
				return method.invoke(person, args);
			} else if (method.getName().equals("setHotOrNotRating")) {
				throw new IllegalAccessException();
			} else if (method.getName().startsWith("set")) {
				return method.invoke(person, args);
			}
		} catch (InvocationTargetException e) {
			e.printStackTrace();
		}
		return null;
	}
}

class PersonBeanImpl implements PersonBean {
	String name;
	String gender;
	String interests;
	int rating;
	int ratingCount = 0;

	public String getName() {
		return name;
	}

	public String getGender() {
		return gender;
	}

	public String getInterests() {
		return interests;
	}

	public int getHotOrNotRating() {
		if (ratingCount == 0)
			return 0;
		return (rating / ratingCount);
	}

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

	public void setGender(String gender) {
		this.gender = gender;
	}

	public void setInterests(String interests) {
		this.interests = interests;
	}

	public void setHotOrNotRating(int rating) {
		this.rating += rating;
		ratingCount++;
	}
}

interface PersonBean {

	String getName();

	String getGender();

	String getInterests();

	int getHotOrNotRating();

	void setName(String name);

	void setGender(String gender);

	void setInterests(String interests);

	void setHotOrNotRating(int rating);

}

public class MyProxy {
	HashMap<String, PersonBean> datingDB = new HashMap<String, PersonBean>();

	public static void main(String[] args) {
		MyProxy test = new MyProxy();
		test.drive();
	}

	public MyProxy() {
		initializeDatabase();
	}

	public void drive() {
		PersonBean joe = getPersonFromDatabase("Joe Javabean");
		PersonBean ownerProxy = getOwnerProxy(joe);
		System.out.println("Name is " + ownerProxy.getName());
		ownerProxy.setInterests("bowling, Go");
		System.out.println("Interests set from owner proxy");
		try {
			ownerProxy.setHotOrNotRating(10);
		} catch (Exception e) {
			System.out.println("Can't set rating from owner proxy");
		}
		System.out.println("Rating is " + ownerProxy.getHotOrNotRating());

		PersonBean nonOwnerProxy = getNonOwnerProxy(joe);
		System.out.println("Name is " + nonOwnerProxy.getName());
		try {
			nonOwnerProxy.setInterests("bowling, Go");
		} catch (Exception e) {
			System.out.println("Can't set interests from non owner proxy");
		}
		nonOwnerProxy.setHotOrNotRating(3);
		System.out.println("Rating set from non owner proxy");
		System.out.println("Rating is " + nonOwnerProxy.getHotOrNotRating());
	}

	PersonBean getOwnerProxy(PersonBean person) {

		return (PersonBean) Proxy.newProxyInstance(person.getClass().getClassLoader(),
				person.getClass().getInterfaces(), new OwnerInvocationHandler(person));
	}

	PersonBean getNonOwnerProxy(PersonBean person) {

		return (PersonBean) Proxy.newProxyInstance(person.getClass().getClassLoader(),
				person.getClass().getInterfaces(), new NonOwnerInvocationHandler(person));
	}

	PersonBean getPersonFromDatabase(String name) {
		return (PersonBean) datingDB.get(name);
	}

	void initializeDatabase() {
		PersonBean joe = new PersonBeanImpl();
		joe.setName("Joe Javabean");
		joe.setInterests("cars, computers, music");
		joe.setHotOrNotRating(7);
		datingDB.put(joe.getName(), joe);

		PersonBean kelly = new PersonBeanImpl();
		kelly.setName("Kelly Klosure");
		kelly.setInterests("ebay, movies, music");
		kelly.setHotOrNotRating(6);
		datingDB.put(kelly.getName(), kelly);
	}
}

Console Result

Name is Joe Javabean
Interests set from owner proxy
Can't set rating from owner proxy
Rating is 7
Name is Joe Javabean
Can't set interests from non owner proxy
Rating set from non owner proxy
Rating is 5

Conclusion

N/A