Proxy Pattern

A short description of the software design pattern proxy.

Ever needed to protect a remote object? Did you ever need to provide extra security or additional mechanisms for acessing a target object? With the proxy pattern your possibilities are almost endless.
Let's say you have a class System which can be accessed publicly and can provide sensible information about it to anyone. This is the target object.
So you want to protect the access to this object and you don't want to change the source code. What do you do? You create a proxy for acessing it.
You create a new class, let's say SystemProxy, and from now on, the target object should no longer be accessed publicly and only the proxy knows how to interact with the target object.
You then create the additional mechanism to protect the sensible information, say... only administrators can request that information. You create a method called requestSystemInfo inside of which will be an if clause determining if the user is an admin.
If true, the SystemProxy calls the requestSystemInfo directly to the System object. If false, no method is called.
In this simple way you have protected the access to your target object without changing its source code!
From now, it's up to you as you can add whatever mechanisms you want to your target object.

FEUP 2011/12