An Introduction to proxy design pattern in java

Design Pattern:-

We have 3 types of design patterns.

1. Creational design pattern.
2. Behavioural design pattern. 
3. Structural design pattern.

In this blog, I will show you how we can use the proxy design pattern in java.

The proxy design pattern comes under the structural design pattern category.

Proxy means 'on behalf of' are literal meanings of proxy and that directly explains Proxy Design Pattern.
Proxies are referred to as surrogates, handles, and wrappers. they're closely connected in structure, however not purpose, to Adapters and  designers.

A real world example will be a cheque or card could be a proxy for what's in our bank account. It can be utilized in place of money, and provides a means of accessing that money when needed. And that’s exactly what the Proxy pattern will do – “Controls and manage access to the object they're protecting“.

When to use this pattern?

Proxy pattern is used when we need to create a wrapper to cover the original object’s complexity from the client.

Let's take a look on example.

A very simple real world situation is like college internet, that restricts few web site access. The proxy initial checks the host you're connecting to, if it's not a part of restricted web site list, then it connects to the real internet. This example is based on Protection proxies.

Lets see how it works :

First of all we will create an Internet interface

Internet.java

package com.pavan.demo.proxy; 
  
public interface Internet 
{ 
    public void connectTo(String serverhost) throws Exception; 
}

Now, we will create a class  RealInternet class which will implements Internet Interface

RealInternet.java

package com.pavan.demo.proxy; 

public class RealInternet implements Internet 
{ 
	@Override
	public void connectTo(String serverhost) 
	{ 
		System.out.println("Connecting to "+ serverhost); 
	} 
} 

Now, we are going to create a proxy class as ProxyInternet  which will aslo implements Internet Interface

ProxyInternet.java

package com.pavan.demo.proxy; 

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


public class ProxyInternet implements Internet 
{ 
	private Internet internet = new RealInternet(); 
	private static List bannedSites; 
	
	static
	{ 
		bannedSites = new ArrayList(); 
		bannedSites.add("abc.com"); 
		bannedSites.add("def.com"); 
		bannedSites.add("ijk.com"); 
		bannedSites.add("lnm.com"); 
	} 
	
	@Override
	public void connectTo(String serverhost) throws Exception 
	{ 
		if(bannedSites.contains(serverhost.toLowerCase())) 
		{ 
			throw new Exception("Access Denied"); 
		} 
		
		internet.connectTo(serverhost); 
	} 

} 

Now , we will create a client class to test 

Client.java

package com.pavan.demo.proxy; 

 public class Client 
{ 
	public static void main (String[] args) 
	{ 
		Internet internet = new ProxyInternet(); 
		try
		{ 
			internet.connectTo("oodlestechnologies.com"); 
			internet.connectTo("abc.com"); 
		} 
		catch (Exception e) 
		{ 
			System.out.println(e.getMessage()); 
		} 
	} 
} 
 

As  abc.com is  mentioned in the banned sites, So the 

Output :

Connecting to oodlestechnologies.com

Access Denied

Drawbacks of proxy pattern:

This pattern introduces another layer of abstraction that generally is also a problem if the RealSubject code is accessed by a client directly and a few of them would possibly access the Proxy classes. This would possibly cause disparate behaviour.

Thanks.