State

• Intent: Provide a surrogate or placeholder for another object to control access to it.
• Also known as “Surrogate”.
• Here are several common situations in which the Proxy pattern is applicable:
  • A remote proxy provides a local representative for an object in a different address space.
  • A virtual proxy creates expensive objects on demand.
  • A protection proxy controls access to the original object. Protection proxies are useful when objects should have different access rights.
  • A smart reference is a replacement for a bare pointer that performs additional actions when an object is accessed.

General Structure

Example

In my example the participants are represented as following:

• Subject: ThirdPartyPhotoLibrary
• RealSubject: ThirdPartyPhotoLibraryImpl
• Proxy: PhotoCacheProxy

Some examples in standard Java libraries include:

• java.lang.reflect.Proxy
• javax.ejb.EJB
• javax.inject.Inject

Pros/Cons

Pros ❤️

• You can control the service object without clients knowing about it.
• The proxy works even if the service object isn’t ready or is not available.
• Open/Closed Principle - You can introduce new proxies without changing the service or clients.

Cons 💔

• The response from the service might get delayed.