Design Strategy Utilizing Intermediaries for Flexible Object Integration

In the realm of software development, the Proxy Design Pattern is a valuable tool that helps control access and optimize resource utilization, particularly in the context of image loading in applications.

The Proxy Design Pattern is a structural design pattern that employs a proxy object to manage access to a real object. This pattern is exemplified by a scenario where the Proxy controls the access and loading of images in an application, thereby optimizing the image loading process.

The Components of the Proxy Design Pattern

The Proxy Design Pattern consists of three main components: Subject, RealSubject, and Proxy.

The Subject is an interface or an abstract class that declares the common interface shared by the RealSubject and Proxy. In our example, this could be an interface that defines methods for loading and displaying images.

The RealSubject is the actual object that the Proxy represents. It contains the real implementation of the business logic or the resource that the client code wants to access. In this case, the RealSubject would be the RealImage class, which implements the interface and provides concrete implementations for loading and displaying images from disk.

The Proxy acts as a surrogate for the RealSubject. It implements the same interface as the RealSubject and maintains a reference to the real image object. It checks whether the real image has been loaded and creates a new instance if necessary. The Proxy provides additional functionality such as lazy loading, access control, or logging.

Implementing the Proxy Design Pattern

To implement the Proxy Design Pattern, follow these steps:

Create the Real Object Interface (in our case, the interface for loading and displaying images).
Create the Real Object (the RealImage class in our example).
Create the Proxy Class (the ProxyImage class in our example).
Have the client use the Proxy instead of the Real Object.

In our example, the ProxyImage class holds a reference to a real Image object, loading the image from disk only when the display method is called for the first time and reusing the cached image thereafter. This approach, known as lazy loading, avoids unnecessary loading and improves performance.

Chaining Proxies

The Proxy Design Pattern can be extended by chaining proxies. This means connecting them in a sequence, where each proxy adds its behavior or checks before passing the request to the next proxy or the real object.

When to Use a Proxy

Use a proxy when you want to postpone the creation of a resource-intensive object, control and manage access to an object, optimize resource utilization, interact with objects in distributed systems, or add security layers.

However, avoid using a proxy for simple objects or operations, unnecessary abstraction, performance impact, when access control isn't needed, or when eager loading is acceptable.

In conclusion, the Proxy Design Pattern is a versatile tool in software development, providing ways to control access, add functionality, or optimize performance in various scenarios, including lazy loading, access control, protection, caching, logging & monitoring, and more.