📅Week-5 (Day -1) - Understanding the Proxy Design Pattern: Virtual, Protection, and Remote Proxies Explained

NOTE: - I started my 8-week system design journey with Coder Army. I will be journaling every day, recording what I learn, reflecting on it, and sharing it with my network to help newcomers to system design.

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💠 What is the Proxy Design Pattern?

The Proxy Pattern provides a surrogate or placeholder for another object to control access to it. It’s like a personal assistant who filters or manages your meetings. ☎️🙅‍♂️

(Hindi: Proxy Pattern ek aisa design pattern hai jo kisi object ke liye ek representative ya agent banata hai — jo us object ka access control karta hai.)

💠 Why Do We Need a Proxy?

• Sometimes, direct access to an object is too expensive, unsafe, or just not possible.

• Proxies help in handling:

  • 💰 Expensive resource usage

  • 🔐 Security and protection

  • 🌍 Remote objects access

💠 Types of Proxy

1️⃣ Virtual Proxy – Lazy Loading

Use Case: Delays the creation of an expensive object until it’s needed.

Example: Imagine a photo gallery app. You don’t want to load all high-res images at once — instead, use a proxy that loads them when scrolled into view.

(Hindi: Agar koi image bahut heavy hai toh usse turant load karne ke bajaye tab load karo jab user use dekhe — yeh kaam karta hai virtual proxy.)

interface IImage {
    void display();
}

class RealImage implements IImage {
    private String filename;

    public RealImage(String file) {
        this.filename = file;
        System.out.println("[RealImage] Loading image from disk: " + filename);
    }

    @Override
    public void display() {
        System.out.println("[RealImage] Displaying " + filename);
    }
}

class ImageProxy implements IImage {
    private RealImage realImage;
    private String filename;

    public ImageProxy(String file) {
        this.filename = file;
        this.realImage = null;
    }

    @Override
    public void display() {
        if (realImage == null) {
            realImage = new RealImage(filename);
        }
        realImage.display();
    }
}

public class VirtualProxy {
    public static void main(String[] args) {
        IImage image1 = new ImageProxy("sample.jpg");
        image1.display();
    }
}

2️⃣ Protection Proxy – Access Control

Use Case: Controls access to sensitive objects based on permissions.

Example: Admin dashboard. Only admins can delete data — others can only view. Protection Proxy checks user role before allowing actions.

(Hindi: Jaise bank ke admin panel mein sirf authorised log hi kuch edit kar sakte hain — normal users nahi. Yeh kaam karta hai protection proxy.)

interface IDocumentReader {
    void unlockPDF(String filePath, String password);
}

class RealDocumentReader implements IDocumentReader {
    @Override
    public void unlockPDF(String filePath, String password) {
        System.out.println("[RealDocumentReader] Unlocking PDF at: " + filePath);
        System.out.println("[RealDocumentReader] PDF unlocked successfully with password: " + password);
        System.out.println("[RealDocumentReader] Displaying PDF content...");
    }
}

class User {
    public String name;
    public boolean premiumMembership;

    public User(String name, boolean isPremium) {
        this.name = name;
        this.premiumMembership = isPremium;
    }
}

class DocumentProxy implements IDocumentReader {
    private RealDocumentReader realReader;
    private User user;

    public DocumentProxy(User user) {
        this.realReader = new RealDocumentReader();
        this.user = user;
    }

    @Override
    public void unlockPDF(String filePath, String password) {
        if (!user.premiumMembership) {
            System.out.println("[DocumentProxy] Access denied. Only premium members can unlock PDFs.");
            return;
        }
        realReader.unlockPDF(filePath, password);
    }
}

public class ProtectionProxy {
    public static void main(String[] args) {
        User user1 = new User("Rohan", false);
        User user2 = new User("Rashmi", true);

        System.out.println("== Rohan (Non-Premium) tries to unlock PDF ==");
        IDocumentReader docReader = new DocumentProxy(user1);
        docReader.unlockPDF("protected_document.pdf", "secret123");

        System.out.println("\n== Rashmi (Premium) unlocks PDF ==");
        docReader = new DocumentProxy(user2);
        docReader.unlockPDF("protected_document.pdf", "secret123");
    }
}

3️⃣ Remote Proxy – Object Over the Internet

Use Case: Represents an object that exists remotely (e.g., on a different server).

Example: When your app calls an API hosted in the US while you're in India. The Remote Proxy acts as a local placeholder.

(Hindi: Jaise Zoom call mein aapka friend US mein hai, lekin aap usse proxy ke through local screen par dekh rahe ho.)

interface IDataService {
    String fetchData();
}

class RealDataService implements IDataService {
    public RealDataService() {
        // Imagine this connects to a remote server or loads heavy resources.
        System.out.println("[RealDataService] Initialized (simulating remote setup)");
    }

    @Override
    public String fetchData() {
        return "[RealDataService] Data from server";
    }
}

// Remote proxy
class DataServiceProxy implements IDataService {
    private RealDataService realService;

    public DataServiceProxy() {
        realService = new RealDataService();
    }

    @Override
    public String fetchData() {
        System.out.println("[DataServiceProxy] Connecting to remote service...");
        return realService.fetchData();
    }
}

public class RemoteProxy {
    public static void main(String[] args) {
        IDataService dataService = new DataServiceProxy();
        dataService.fetchData();
    }
}

💠Real-World Use Cases

• 🎮 Lazy loading in games (Virtual Proxy)

• 🔐 Secure APIs or Admin UIs (Protection Proxy)

• 🛰️ Remote object communication (Remote Proxy)

(Hindi: Proxy ka use har jagah hota hai — APIs, games, secure dashboards, aur remote connections mein!)

💠 Benefits of Proxy Pattern

• Lazy initialization of heavy resources

• Improved security and access control

• Enables distributed computing

• Cleaner client-side code

💠Recap

Proxy Pattern kya karta hai?

Kisi object ka access control karta hai ek mediator ya representative ke through.

Types of Proxy

1. Virtual Proxy → Jab zarurat ho tab load karo

2. Protection Proxy → Sirf authorized users ko access do

3. Remote Proxy → Door ke object ko local bana do

(Hindi: Proxy Pattern ek aise concept hai jo aapke project ko smart aur efficient banata hai.)

Week - 5 (Day-1) Completed ✅ System Design

NOTE : - A big thanks to my mentors Rohit Negi Sir and Aditya Sir for launching this amazing 8-week course absolutely free on YouTube via CoderArmy9 :- youtube.com/@CoderArmy9 . 🙌

👉 Share this blog with your connections! Let’s keep learning, growing, and supporting one another on this journey. 🚀

✍️ Payal Kumari 👩‍💻

Jai Hind 🇮🇳 | #CoderArmy #LearningInPublic #SystemDesign #TechForAll #MentorshipMatters #8weeksLLdChallenge #LowLevelDesign #Code #LLD #OOP