Proxy Design Pattern Example

Proxy Design Pattern

The definition of Proxy pattern  provided by Gang of Four book on Design Patterns states:
"Provide a surrogate or placeholder for another object to control access to it."

• Proxy design pattern is one of Structural Design Pattern.
• This design pattern is used to create a surrogate or wrapper "in place of" another object.
• We can modify the functionalities of an object without modifying the actual object’s behavior.  
• The Surrogate or wrapper object is known as proxy of actual object. So we have access controls to actual object.

Q- When to use Proxy Design Pattern ?

• We can use Proxy design pattern when there is a requirement to access control to an Object.
• when there is a need for a reference to an Object.
• If we want to add/modify the object’s behavior without affecting actual object’s behavior.  

There are 4 common situations we can use proxy design pattern.

• Remote proxy:
• Virtual proxy
• Protection proxy:
• Smart Proxy

CollegeInternet.java

package com.shubh.dp.example;

public interface CollegeInternet {
 public void getInternet();
}

CollegeInternetImpl

package com.shubh.dp.example;

public class CollegeInternetImpl implements CollegeInternet {
 private String department;

 public CollegeInternetImpl(String detpName) {
  this.department = detpName;
 }

 @Override
 public void getInternet() {
  System.out.println("Internet has been connected successfully for Department: " + department);
 }
}

InternetProxy.java

package com.shubh.dp.example;

import java.util.ArrayList;
import java.util.List;

public class InternetProxy implements CollegeInternet {
 private String department;
 private CollegeInternet realObject;
 private List proxyLock = new ArrayList();

 public InternetProxy(String department) {
  this.department = department;
 }

 @Override
 public void getInternet() {
  if (!getProxyLock().contains(department)) {
   realObject = new CollegeInternetImpl(department);
   realObject.getInternet();
  } else {
   System.out.println("Internet access not permitted to Department: " + department);
  }
 }

 /* Add the department you want to block */
 public List getProxyLock() {
  proxyLock.add("Math");
  proxyLock.add("Physics");
  proxyLock.add("Chemistry");
  // proxyLock.add("Biology");
  proxyLock.add("Psychology");
  proxyLock.add("Sociology");
  // proxyLock.add("Computer");
  // proxyLock.add("Accounts");
  return proxyLock;
 }
}

ProxyDesignPattern.java

package com.shubh.dp.example;

public class ProxyDesignPattern {
 public static void main(String[] args) {

  /* Access Internate without Proxy */
  // System.out.println("Access Internate without Proxy.");
  CollegeInternetImpl realObject = new CollegeInternetImpl("Math");
  realObject.getInternet();

  /* Access Internate using Proxy */
  // System.out.println("Access Internate using Proxy.");
  InternetProxy internet = new InternetProxy("Math");
  internet.getInternet();

  /* Access Internate using Proxy */
  // System.out.println("Access Internate using Proxy.");
  InternetProxy internetAcc = new InternetProxy("Accounts");
  internetAcc.getInternet();
 }
}

Output:

Internet has been connected successfully for Department: Math
Internet access not permitted to Department: Math
Internet has been connected successfully for Department: Accounts