Proxy Design Pattern: Controlling Object Access and Usage

The Proxy design pattern is a structural pattern that provides a surrogate or placeholder object to control access to another object. The Proxy acts as an intermediary between the client and the real object, allowing for additional functionality, such as access control, caching, or lazy initialization. The Proxy pattern enhances the security, performance, and flexibility of the system.

Key Components of the Proxy Pattern

1. Subject: The Subject is the common interface or abstract class shared by both the Proxy and the Real Object. It defines the operations that the Proxy can perform on behalf of the Real Object.
2. Real Object: The Real Object is the actual object that the Proxy represents. It implements the operations defined by the Subject interface.
3. Proxy: The Proxy class implements the Subject interface and maintains a reference to the Real Object. It controls access to the Real Object and adds additional functionality, such as access control, caching, or lazy initialization.

Example:

Proxy Pattern in Building Access Control: Let’s consider a scenario where we want to control access to certain building objects based on user permissions. We can use the Proxy pattern to create a BuildingProxy that acts as a surrogate for the Building objects and implements access control.

interface Building {
    void enter();
}

class RealBuilding implements Building {
    private String buildingName;

    public RealBuilding(String buildingName) {
        this.buildingName = buildingName;
        System.out.println("Creating Real Building: " + buildingName);
    }

    @Override
    public void enter() {
        System.out.println("Entering Real Building: " + buildingName);
    }
}

class BuildingProxy implements Building {
    private String buildingName;
    private RealBuilding realBuilding;

    public BuildingProxy(String buildingName) {
        this.buildingName = buildingName;
        System.out.println("Creating Building Proxy: " + buildingName);
    }

    @Override
    public void enter() {
        if (checkAccess()) {
            if (realBuilding == null) {
                realBuilding = new RealBuilding(buildingName);
            }
            realBuilding.enter();
        } else {
            System.out.println("Access denied. You don't have permission to enter the building: " + buildingName);
        }
    }

    private boolean checkAccess() {
        // Access control logic
        // Return true or false based on user permissions
        return true; // Placeholder implementation
    }
}

In the above example, we have the Building interface that defines the common operations for entering a building. The RealBuilding class represents the actual building object. The BuildingProxy class serves as the Proxy, implementing the Building interface and controlling access to the RealBuilding object.

The BuildingProxy maintains a reference to the RealBuilding object and checks user permissions before allowing access to the building. If the user has the required permissions, the BuildingProxy creates an instance of the RealBuilding object (if it doesn’t exist) and delegates the enter() operation to it. Otherwise, it denies access.

By using the Proxy pattern, we can control access to building objects and add additional functionality, such as access control, logging, or caching. The Proxy acts as a secure intermediary, providing a controlled interface for clients to interact with building objects.

Benefits and Use Cases of the Proxy Design Pattern

The Proxy design pattern offers several benefits:

1. Access Control: The Proxy pattern enables access control to objects, allowing for enhanced security and permissions-based operations.
2. Performance Optimization: The Proxy pattern can improve performance by adding caching or lazy initialization. It allows the Proxy to perform operations only when necessary, reducing unnecessary computations or resource utilization.
3. Simplified Interface: The Proxy pattern provides a simplified interface to the Real Object, abstracting complex operations or interactions.
4. Modularity and Extensibility: The Proxy pattern promotes modularity by separating the client code from the Real Object. This makes it easier to extend or modify the functionality of the system without impacting the client code.

The Proxy pattern finds use in various scenarios, including:

• Remote Communication: Proxies can be used to communicate with remote objects or services, acting as a local representation of the remote entity.
• Caching: Proxies can be employed to cache expensive or resource-intensive operations, providing faster access to the cached results.
• Access Control: Proxies are useful in scenarios where fine-grained access control is required, allowing the Proxy to verify user permissions before granting access to the Real Object.
• Logging and Auditing: Proxies can add logging or auditing functionality, capturing the interactions between clients and the Real Object for monitoring or debugging purposes.

Conclusion

The Proxy design pattern serves as a powerful tool for controlling access to objects and adding additional functionality. By acting as a surrogate or placeholder, the Proxy enhances security, performance, and flexibility in the system.

In this blog post, we explored the Proxy pattern and its practical application in the context of building construction. Using the example of a BuildingProxy that controls access to building objects based on user permissions, we demonstrated how the Proxy pattern provides secure and controlled interactions with objects.

By leveraging the Proxy design pattern, software engineers and architects can enhance the access control and functionality of objects in various domains beyond building construction. Whether it’s securing sensitive data, optimizing resource utilization, or adding logging capabilities, the Proxy pattern offers a versatile approach.

The Proxy pattern promotes modular and extensible designs by separating the client code from the actual object implementation. This separation allows for future enhancements and modifications to the system without impacting the client code. It also provides a clean and simplified interface, shielding clients from the complexities of the Real Object.

In conclusion, the Proxy design pattern provides a flexible and secure means of controlling access to objects and adding additional features. By leveraging the power of proxies, developers can enhance security, improve performance, and achieve modular designs. So, the next time you encounter a scenario that requires access control or additional functionality for objects, consider applying the Proxy pattern to elevate your system’s capabilities.