Proxy (aka Surrogate)

Intent

• Provide a surrogate or placeholder for another object to control access to it.

Problem

• How can the access to an object be controlled?

• How can additional functionality be provided when accessing an object?

Solution

• Define a separate Proxy object that acts as substitute for another object (Subject).

• Work through a Proxy object to control the access to a real subject.

Types of Proxy

• Remote Proxy

• Virtual Proxy

• Protection Proxy

• Caching Proxy

• Smart Proxy

Advantages

✅ You can control the service object without clients knowing about it. ✅ You can manage the lifecycle of the service object when clients don’t care 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.

Disadvantages

❌ The code may become more complicated since you need to introduce a lot of new classes. ❌ The response from the service might get delayed.

Notes

• Proxy pattern is also known as Surrogate pattern.

• Some common operations done through proxy pattern includes,

  • May hide information about the real object to the client.

  • May perform optimization like on demand loading.

  • May do additional house-keeping job like audit tasks.

• Decorator v/s Proxy