The Proxy pattern is used in real-world applications whenever you need to control access to an object that's expensive to create, remote, or requires permission checks, without changing how client code interacts with it.
Key Points: • A virtual proxy defers creating a resource-heavy object (e.g., a large image or dataset) until it's actually accessed. • A remote proxy represents an object living on another server, handling the network communication transparently for the client. • A protection proxy enforces authentication or authorization checks before forwarding a call to the real object. • A caching proxy stores results of expensive calls and returns cached data for repeated requests. • Java's built-in dynamic proxies (java.lang.reflect.Proxy) and libraries like Spring AOP use this pattern to add cross-cutting behavior such as transactions or security checks around beans.
Example: Spring's @Transactional annotation works by wrapping the target bean in a proxy that opens a transaction before the method runs and commits or rolls it back afterward, all invisible to the calling code.
Interview Tip: A concise interview answer is:
"I'd use a proxy any time I need to control access to something expensive, remote, or permission-gated without the client noticing — a virtual proxy for lazy loading, a remote proxy for distributed objects, or a protection proxy for access checks. It's also what's under the hood of Spring AOP, where @Transactional or @Secured wraps a bean in a proxy that adds behavior around the real method call."