**Course Title:** Software Design Principles: Foundations and Best Practices **Section Title:** Structural Patterns **Topic:** Proxy Pattern **Introduction** In the previous topic, we explored the Composite Pattern, which helps to create tree-like structures of objects. Now, we'll dive into the Proxy Pattern, a structural design pattern that allows you to create an object that acts as a substitute for a real object, controlling access to it. This pattern is useful when you need to optimize or secure the access to the real object. **What is the Proxy Pattern?** The Proxy Pattern is a design pattern that provides a surrogate or placeholder for another object to control access to it. It sits between the client and the real object, intercepting requests from the client and forwarding them to the real object. This pattern helps to delegate, implement, and sometimes control access to the real object. **Types of Proxies** There are three main types of proxies: 1. **Remote Proxy**: Acts as an intermediary between a client on one machine and a server on another machine. It helps to reduce the latency of remote calls. 2. **Virtual Proxy**: Lazy-loads the real object when the client requests it, reducing memory usage and improving performance. 3. **Protection Proxy**: Controls access to the real object based on user credentials or permissions. **How to Implement the Proxy Pattern** To implement the Proxy Pattern, you'll need to create a proxy object that receives requests from the client and forwards them to the real object. The proxy object should have the same interface as the real object. Here's an example implementation in Java: ```java // Real Object public class RealImage { private String filename; public RealImage(String filename) { this.filename = filename; loadFromDisk(filename); } private void loadFromDisk(String filename) { System.out.println("Loading " + filename); } public void display() { System.out.println("Displaying " + filename); } } // Proxy Object public class ProxyImage { private RealImage realImage; private String filename; public ProxyImage(String filename) { this.filename = filename; } public void display() { if (realImage == null) { realImage = new RealImage(filename); } realImage.display(); } } // Client Code public class Client { public static void main(String[] args) { ProxyImage image1 = new ProxyImage("image1.jpg"); ProxyImage image2 = new ProxyImage("image2.jpg"); image1.display(); // Loads the image from disk image2.display(); // Loads the image from disk image1.display(); // Uses the cached image image2.display(); // Uses the cached image } } ``` In this example, the `ProxyImage` class acts as a proxy for the `RealImage` class, loading the image from disk only when it's requested by the client. **Benefits and Use Cases** The Proxy Pattern provides several benefits: * **Lazy Loading**: Reduces memory usage and improves performance by loading the real object only when requested. * **Caching**: Improves performance by caching the results of expensive operations. * **Access Control**: Allows you to control access to the real object based on user credentials or permissions. * **Load Balancing**: Helps to distribute the load across multiple servers. Use cases for the Proxy Pattern include: * **Web servers**: Use proxies to cache frequently requested resources, reducing the load on the server. * **Database connections**: Use proxies to control access to database connections and improve performance. * **File access**: Use proxies to optimize file access and reduce memory usage. **Conclusion** The Proxy Pattern is a useful structural pattern that helps to optimize and secure access to real objects. By creating a surrogate or placeholder for the real object, you can control access, reduce memory usage, and improve performance. Remember to consider the different types of proxies and use cases when deciding whether to implement this pattern in your design. **What's Next?** In the next topic, we'll explore the Observer Pattern, a behavioral pattern that helps to notify objects about changes to other objects. **External Resources** * [Java Design Patterns: Proxy Pattern](https://www.tutorialspoint.com/design_pattern/proxy_pattern.htm) * [Proxy Pattern](https://en.wikipedia.org/wiki/Proxy_pattern) **Comments and Questions** If you have any questions or comments about this topic, please leave a comment below.