Design Pattern #11: The Proxy Pattern

These are my notes for the book Headfirst Design Patterns.

Example

Monitor gumball machine remotely.

• Java's RMI:
  • client object --> client helper (proxy, "stub") --> service helper ("skeleton") --> service object
  • RMI: build client helper + service helper
  • steps:
    • make a remote interface: defines available remote methods
    • make a remote implementation (aka remote service)
    • create stub and skeleton using rmic (both proxy and real object use same interface)
    • start rmi registry
    • start remote service
  • client: does a lookup on RMI registry, RMI registry deserialize and return the stub object. (client must have the stub class, although it always uses the remote interface)

Definition

• Provides a surrogate or placeholder for another object to control access to it. Maybe remote, expensive to create (virtual proxy) or in need of securing.
• Control and manage access
• Remote proxy: acts as a local representative to a remote object.
• Virtual proxy: delegate requests directly to object after it is created.
• Protection proxy: invocationHandler decides what method to call on actual object.