Overview
This lecture introduces the proxy design pattern, its use in networking and programming, and explains how proxies can control access, provide security, and add new functionality such as caching.
Proxy Servers in Networking
- A proxy server is an intermediary that separates end-users from the destinations they browse.
- Traffic flows through the proxy server, which forwards requests and responses between user and website.
- Proxies can act as firewalls, web filters, shared connection managers, and cache data for faster access.
- Proxies enhance privacy and security for users and internal networks.
Proxy Pattern in Software Design
- The proxy pattern is a structural design pattern that provides a substitute or placeholder for another object.
- It controls access to the original object, performing actions before or after requests reach the object.
Proxy Pattern Examples
- Restricting access: A proxy can block user requests to banned websites by checking against a blacklist before forwarding.
- Caching: A proxy for a VideoDownloader class can cache downloaded videos, serving repeated requests from cache instead of downloading again.
Structure of Proxy Pattern
- The Service interface defines the operations performed (e.g., Internet, VideoDownloader).
- The Real Service class implements the actual business logic (e.g., RealInternet, RealVideoDownloader).
- The Proxy class implements the same interface and holds a reference to a real service object, adding extra behavior.
- The Client uses the interface, so it can work with both proxies and real service objects interchangeably.
Benefits of Proxy Pattern
- Allows control over access to objects by inserting logic before/after requests.
- Enables substituting proxies without changing client or service code (open-closed principle).
- Proxies can manage service object lifecycles and function even if the service isn't ready or available.
Key Terms & Definitions
- Proxy Server — intermediary server separating users from destination servers, offering privacy and security.
- Proxy Pattern — design pattern substituting a real object to control access or add functionality.
- Caching — storing data to quickly serve future requests without recomputing or redownloading.
- Open-Closed Principle — a design principle where classes can be extended without modifying their source code.
Action Items / Next Steps
- Review the class diagram of the proxy pattern and relate it to given examples.
- Practice implementing a simple proxy pattern in code.