Proxy Design Pattern

Definition

A Structural Design Pattern which controls the access to a heavy resource extensive object by providing surrogate object that has similar method.

Intention

1. Can be used to control the access to an Object
2. Deters the creation of heavy object until it required completely
3. Reduces the number of actual object calls providing a surrogate object

Component

Subject - The common interface that implements both real and proxy objects.
Real Object - The actual object that client needs to work with.
Proxy - The object client is provided to represent the actual object hiding the complexity.
Client - The user who needs to interact with the Subject.


















Subject

public interface Loader {

    public void getFile();
}


Real Object

public class FileLoader implements Loader {
    @Override
    public void getFile(){
       
        System.out.println("Accessing the file");
    }

}
 
Proxy Object

public class ProxyFileLoader implements Loader {

    private FileLoader fileLoader;
    private boolean isAutorized;

    public ProxyFileLoader(String userName, String password) {

        if ("userA".equalsIgnoreCase(userName)
                && "passwordA".equalsIgnoreCase(password)) {
            setAutorized(true);
        }
        fileLoader = new FileLoader();
    }

    @Override
    public void getFile() {
        if (isAutorized) {
            fileLoader.getFile();
        }

        else {
            System.out.println("Cannot access the file.");
        }
    }

    public boolean isAutorized() {
        return isAutorized;
    }

    public void setAutorized(boolean isAutorized) {
        this.isAutorized = isAutorized;
    }

}

Client

public class Client {

    public static void main(String[] args) {

        Loader loader = new ProxyFileLoader("userA", "passwordA");
        loader.getFile(); // Output: Accessing the file

        Loader loaderWithIncorrectCredintials = new ProxyFileLoader(
                "wrongUser", "wrongPassword");
        loaderWithIncorrectCredintials.getFile(); // Output: Cannot access the file.
                                                   
    }

}