Scenario

Problem

Don't want to change the functionality of the action()
But you may want to change some of the non-functional features of it
Adding additional features means changing the Subject
Want to do so flexibly, i.e., opportunistically add additional features on how the functionality is delivered
This may mean caching, protection, etc.

Proxy

Proxy Pattern

Proxy Pattern

Changes the behavior of the service but preserves the interface
Delegate action to another class
Client uses the proxy just like it was the real thing (in general)

Adapter vs. Proxy

Examples

Examples

Virtual Proxy Provides a placeholder for an expensive object, delaying its instantiation until it is needed, e.g., a large image that is loaded only when it becomes visible on the screen
Remote Proxy Represents an object in a different address space, e.g., a client accessing a remote database through a remote proxy
Protection Proxy Controls access to the original object based on specific permissions or authentication, e.g., a proxy that checks user access rights before granting access to a secured system
Cache Proxy Stores the results of expensive operations and returns cached results, e.g., a web proxy caching server that stores frequently accessed web pages to reduce load times
Firewall Proxy Protects a network from unauthorized access by filtering incoming and outgoing traffic, e.g., a proxy server that examines packets and determines whether they should be allowed through the network
Smart Reference Proxy Adds extra behavior when an object is accessed, like reference counting, e.g., a proxy that keeps track of the number of times an object is accessed
Logging Proxy Adds logging functionality to an object's operations for debugging or auditing purposes, e.g., a proxy that logs requests made to a web service
Synchronization Proxy Provides thread-safe access to a shared resource by controlling concurrent access, e.g., a proxy that ensures only one thread can access a shared data structure at a time

Protection Proxy

Chains of Proxies