JAVA EXAMPLE PROGRAMS

JAVA EXAMPLE PROGRAMS

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Proxy Design Pattern in java


Proxy design pattern is very simple, but very effective. Proxy pattern provide a surrogate or placeholder for another object to control access to it.

Proxy design pattern allows us to create a wrapper class over real object. Wrapper class which is proxy, controls access to real object so in turn we can add extra functionalities to real object without changing real object's code. A very simple real life scenario is our office internet, which restricts few site access. The proxy first checks the host you are connecting to, if it is not part of restricted site list, then it connects to the real internet.

There are four common situations in which the Proxy pattern is applicable:

1) A remote proxy provides a local representative for an object that resides in a different address space. This is what the "stub" code in RPC and CORBA provides.

2) A virtual proxy is a placeholder for "expensive to create" objects. The real object is only created when a client first requests/accesses the object.

3) A protective proxy controls access to a sensitive master object. The "surrogate" object checks that the caller has the access permissions required prior to forwarding the request.

4) A smart proxy interposes additional actions when an object is accessed.

Here is the code for proxy pattern.

package com.java2novice.dp.proxy;

public interface Internet {

	public void connectTo(String host) throws Exception;
}

Real internet class

package com.java2novice.dp.proxy;

public class RealInternet implements Internet {

	@Override
	public void connectTo(String host) {
		System.out.println("Connecting to "+host);
	}
}

Proxy internet class

package com.java2novice.dp.proxy;

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

public class InternetProxy implements Internet {

	private Internet internet = new RealInternet();
	private static List<String> restrictedSites;
	
	static {
		restrictedSites = new ArrayList<String>();
		restrictedSites.add("jumbxyz.com");
		restrictedSites.add("testme.com");
		restrictedSites.add("adult-site.com");
		restrictedSites.add("bad-site.com");
	}
	
	@Override
	public void connectTo(String host) throws Exception {
		
		if(!restrictedSites.contains(host.toLowerCase())){
			internet.connectTo(host);
		}
		throw new Exception("Company restricted this site view");

	}

}

proxy demo class

package com.java2novice.dp.proxy;

public class ProxyDemo {

	public static void main(String a[]){
		
		Internet intConn = new InternetProxy();
		try {
			intConn.connectTo("java2novice.com");
			intConn.connectTo("adult-site.com");
		} catch (Exception e) {
			System.out.println(e.getMessage());
		}
	}
}

Output:
Connecting to java2novice.com
Company restricted this site view
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Java design pattern examples

  1. Factory Pattern
  2. Abstract Factory Pattern
  3. Builder Design Pattern
  4. Prototype Pattern
  5. Adapter Pattern
  6. Composite Pattern
  7. Proxy Pattern
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Knowledge Centre
What is abstract class or abstract method?
We cannot create instance for an abstract class. We can able to create instance for its subclass only. By specifying abstract keyword just before class, we can make a class as abstract class.

public abstract class MyAbstractClass{

}

Abstract class may or may not contains abstract methods. Abstract method is just method signature, it does not containes any implementation. Its subclass must provide implementation for abstract methods. Abstract methods are looks like as given below:

public abstract int getLength();
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About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected].

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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java™ Platform Standard Ed. 8 - API Specification | Java is registered trademark of Oracle.
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