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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
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