In the realm of software development and design patterns, a Proxy is a structural design pattern. It is used to provide a substitute for another object in order to control access to it. Essentially, it acts as an intermediary that serves as an interface to another resource, handling requests directed to the original object.
Understanding the Proxy Pattern
The Proxy pattern acts as a placeholder or surrogate for another object. It intercepts calls to the real subject and adds some logic or behavior before or after forwarding the call to the real object. This control over access can be used for various purposes.
Key Characteristics:
- A proxy maintains a reference that lets it access the real subject.
- It implements the same interface as the real subject so that the proxy can be substituted for the real subject.
- The proxy controls access to the real subject and may also be responsible for creating and deleting the real subject.
Why Use a Proxy?
Using a proxy offers several advantages, primarily centered around managing how and when access is granted to an object:
- Control Access: Restrict who or what can access the real object.
- Lazy Initialization: Defer the creation of expensive objects until they are actually needed (Virtual Proxy).
- Remote Objects: Provide a local representative for an object in a different address space (Remote Proxy).
- Protection: Implement security checks before accessing sensitive objects (Protection Proxy).
- Logging and Monitoring: Log method calls or track usage of the real object.
- Caching: Cache results from the real object to improve performance.
Common Types of Proxies
There are several variations of the Proxy pattern, each serving a specific purpose:
- Virtual Proxy: Delays the creation and initialization of an expensive object until requested.
- Remote Proxy: Represents an object that resides in a different address space or on a remote machine.
- Protection Proxy: Controls access to the original object, performing security checks before allowing access.
- Smart Reference: Provides additional actions whenever a reference to the object is made, such as counting the number of references or loading a persistent object into memory.
Proxy vs. Adapter vs. Decorator
While also structural patterns, the Proxy pattern differs from the Adapter and Decorator patterns:
| Pattern | Purpose | Relationship |
|---|---|---|
| Proxy | Controls access to an object. | Acts as a surrogate for the real object. |
| Adapter | Makes an interface compatible with another. | Wraps an existing object. |
| Decorator | Adds responsibilities to an object dynamically. | Wraps an existing object. |
In summary, the Proxy design pattern is a powerful tool for managing interactions with objects, providing a layer of control, optimization, or security by acting as an intermediary.
